Hi everybody,
I'm not pro in any way and I've never been close to rank 1 or Master league, however I'm fast approaching 3000 games played with about 350 of them with Johanna, which is kind of my main, so I believe I have a very decent understanding of her. Go here for my HotsLogs profile.

I really fell in love with Johanna from the first game since she's exactly the kind of character I enjoy - low damage, very high survivability and utility. If you're here to do damage, you may as well forget about playing her, she's not about that. Johanna is all about keeping your team alive while being a pain in the *** for the enemy team.

One of the most important things about Johanna (and about every hero in HotS to be honest) is understanding your role in the team. Each hero is designed for a specific job (sometimes more than one) and in order to play it properly you must understand it.
Johanna is the queen of peels - you job is to keep your team alive by minimizing the incoming damage. Don't try to chase and secure kills during a fight, don't try to push, don't try to pressure their healer, all these just aren't your job. Sure, you often do them when it's the right time, but every moment of play with Johanna you should be asking yourself - How can I minimize the damage my team is taking right now?
And now, lets see how it's done.

Punish [Q] - Slow enemies by 60% decaying over 2 seconds.
This is your highest damage ability (which is still crazy low). You can use it in lane to clear waves faster or on escaping enemies to secure the kill, but don�??t forget you can also use it defensively during team fights to make it harder for the enemy team to reach your squishies. Important - never use it while running away unless you want to sacrifice yourself for the team, since using this ability also makes Johanna take a step forward to the direction it is cast.

Condemn [W] - After 1 second, pull nearby enemies toward you, stunning them for 0.25 seconds.
WOW. This must be Johanna's defining ability. You can do so much with this - set up combos for your mages, disrupt the enemy team's positioning, peel for you teammates by pulling melees away from them, use it for wave clear thanks to Knight takes Pawn's just amazing. Also, keep in mind - even if you are stunned during that 1 second delay after casting, it will still work.

Shield Glare [E] - Blinds enemies in a large cone for 1.5 seconds.
The damage of this ability is meaningless, but the utility is priceless! This ability alone can stop so much incoming damage - so use it wisely. Is Raynor/Valla harassing your team with auto-attacks? Is butcher charging your favorite squishy? Is Illidan diving your healer? Blind them and makes the utterly useless for 1.5 seconds. This alone can be enough to turn the butcher's onslaught into his demise.

Iron Skin [D] - Gain a Shield for 4 seconds. While this Shield is active, you are Unstoppable.
This is even more WOW than condemn. This is the reason you can do what you do - engage for your team, go deep into the enemy team, Condemn them, burn their CCs and cooldowns, make their lives miserable. With practice, you will learn to time it just right for the other team to throw all their things at you and utterly waste their cooldowns and mana. Never use it too early since it has a long cooldown, but make sure not to use it too late since you can be dead by then...

Falling Sword [R1] - You leap towards an area. While in the air, you can steer the landing location by moving. After 2 seconds you land, dealing damage to nearby enemies and knocking them into the air.
This heroic isn't bad, but it's very situational. I only pick this if your team desperately needs someone who can dive the backline and have no one else to do it. Otherwise, the stun is too short and the heroic is too easily dodged. This is also the only escape Johanna has.

Blessed Shield [R2] - Stun the first enemy hit for 1.5 seconds. Blessed Shield then bounces to 2 nearby enemies, stunning them for 0.75 seconds.
This deals less damage than Falling sword, but it's just so much more useful. You can use it to peel, to engage or to disengage and it also has a much shorter cooldown of just 50 seconds. This is my go to heroic in 99% of the time simply because it is so versatile, even after it was nerfed.

I think Johanna is among the heroes with the better talent Choices - nearly ever talent tier has some choice to be made, very little talents are really useless. The build at the top of the page is the cookie-cutter build, but I really recommend you read through this section since there's lots of variability there. The talents are organized in the order of how good I think they are, the first in each tier being the best.

Level 1

Since KtP became baseline, the level 1 talent tier is pretty dull. I don't feel like anything is especially good here.
Regeneration Master - I don't like it so much on Jo, but this if you're not facing strong AAers there's nothing better anyway.
Reinforce - Using basic abilities grants you block charges, up to a maximum of 2. An amazing Block variant. You can easily have 5 block charges in the beginning of a fight if you play smart - 2 charges before you even start and the 3 from using you abilities. If you take Eternal Retaliation and Blessed Momentum you have basically infinite block charges as long as you have mana. Always take this talent against AA heavy teams that have at least 2 strong AAers (Raynor, Hammer, Butcher, Greymane). Remember that you also have a blind - so keep to the blind to save your teammates and the block for yourself.
Righteous Smash - Punish returns 10 mana per enemy hit. One of the most useless talents in Johanna's talent tree. You usually don't have mana issues, and if you do - this won't help. Also, the other talents are way too good.

Level 4

Laws of Hope - Increases your passive health regeneration and can be activated to heal 20% of your maximum health over 4 seconds. This talent is really good for self sustain, since it allows you to have that little extra healing when your healer's heals are on cooldown, and the extra regen is quite nice as well (especially when skipping regen master). If you don't have a healer you can trust, this is a good choice in this tier, but I sill prefer Eternal Retaliation.
Amplified Healing - Great talent if you have a healer you trust, since it makes their life so much easier when healing you. Also synergizes nicely with Holy Renewal at 16.
Eternal Retaliation - The cooldown of Condemn is lowered by 0.75 seconds for each enemy hit up to a reduction of 7.5 seconds. First of all, it is worth mentioning this is the most popular talent taken by professional Johanna players - I see it in tournaments all the time. For a long time I never took it, but ever since I discovered it - I just can't go back. Disregard the wave clear improvement (though it is impactful), the big thing about it is the amount of control it gives you in fights. ESPECIALLY against melee-heavy teams, this gives you incredible amounts of disruption. TRY IT! Also comboes well with Reinforce.
Roar - Increase Punish damage by 50%. Forget about Righteous Smash, this is the most useless talent in the whole tree. You don't do damage and you never will, let it go.

Level 7

Conviction - Your movement speed is increased by 25% while Condemn is charging up. Really useful for engaging, disengaging, helping your team secure kills. I discovered how good this talent is quite late and I never looked back.
Blessed Momentum - Incredible, I always either pick this or Conviction. As you should be using your AAs quite a lot, this means you have all your abilities up more often which is great. Comboes very well with Reinforce. Does not affect the cooldown of Iron Skin!
The Crusade Marches On - Using basic and heroic abilities reduce the cooldown of Iron Skin by 1.5 seconds. It's kinda meh if you ask me - While having Iron Skin more often is nice, you should learn to time it right and play in a way that you don't need it more often than you have it as it is. Also, the other talents are just better.
Sins Exposed - Shield Glare marks enemies for 4 seconds, causing them to take extra damage the next time an ally damages them. Remember what I taught you - Johanna is not about the damage. Move along now.

HEROICS!

- see the abilities section.

Level 13

Burning Rage - Great talent for Johanna, usually my Go To. Seeing how you are always in the thick of things you get so much value out of this. Perfect against melee-heavy comps but also just good in general.
Spell Shield - Another great talent. Take this if you feel like you can't stand the burst from the other team (if they have Chromie+Li Ming for example).
Subdue - Increases the slow from Punish to 80% decaying over 3 seconds. This is a really big thing - since the slow on Punish decays over time, this talent has a cumulative effect that improves it greatly. Pick this talent if you feel you have enough survivability but your team needs help securing kills.
Hold Your Ground - Increases the shield from Iron Skin by 20% and reduces the cooldown by 4 seconds if broken. This is the least useful talent in this tier, but still not bad. Pick this if you feel that you are being heavily focused when engaging the enemy.

Level 16

Holy Renewal - Johanna is healed by every hero affected by Shield Glare. Great talent for self sustain, synergizes well with Amplified Healing, with your trait, with Blessed Momentum and with Indestructible.
Imposing Presence - The new Imposing Presence is AMAZING for Johanna! Between this talent, your blinds and possibly Reinforce on level 1, AAers simply can't hurt you. Take this whenever the enemy team has at least 2 strong AAers (like with Reinforce). Activate it after you pull all the AAers to you with condemn and let your team finish them. Also great for preventing fleeing heroes from escaping. An amazing counter for Samuro as well.
Fanaticism - When Iron Skin is active, increases your movement speed by 8% each time you take damage up to 40%. This talent is a bit dangerous, but it works wonders if you play aggressively. Basically, it's a win more talent.
Blessed Hammer - Condemn also creates a spinning hammer that spirals around you dealing damage. This talent was all the rage when Johanna just came out, but I think it's way overrated. The damage is extremely low and either way - dealing damage is not your job, remember?

Level 20

Indestructible - Upon taking fatal damage, gain a shield for 5 seconds. This talent is no less than amazing, since it pretty much gives you a 2nd life. This together with an Uther with Redemption on your team makes your team so hard to defeat in a late game team fight. I rarely see a reason to take anything other than this. Works especially well with Rehgar's Ancestral Healing.
Storm Shield - Not a bad talent, but usually you already have somebody else on your team who takes it. Can be very useful in some cases, but quite situational.
Radiating Faith - Increases the stun duration of Blessed Shield by 33% and it bounces to 2 additional enemies. Pretty good, as it allows you to stun the entire enemy team and for a longer time, but unless you feel like you've never been even close to death, Indestructible is to good to pass on.
Heaven's Fury - While in the air, rain down holy bolts on the enemies beneath you, reducing the cooldown of Falling Sword by 2 seconds per enemy hit. I rarely take Falling Sword and taking this over Indestructible nearly never happens. Skip it.

Cookie Cutter build: If you're unsure of what to take - start with that. Gives you enough peels and sustain to do you job as a tank. If you're worried about sustain, switch out Eternal Retaliation for Laws of Hope, but I really recommend you try it first.

Anti-AA build: If you're facing 2 or more strong AA heroes (Raynor, Hammer, Greymane, Butcher), this build is great. If they're mostly ranged, switch Eternal Retaliation out for Laws of Hope.
Since Reinforce gives you a block charge every time you use an ability, Eternal Retaliation and Blessed Momentum allow you to have Block charges ALL the time. Once you also get Imposing Presence, AA heroes can't really touch you (as long as you can land your blinds well).
Keep in mind - This is effective against heroes with slow and hard hitting AAs, so it's not effective against Illidan and clearly not against Tracer and Tychus. Another thing to keep in mind is that Eternal Retaliation with Blessed Momentum can make you very mana heavy due to how often you can use your ablities, so don't spam mindlessly.

Anti-mage build: This is quite unorthodox, but I like it. Mages are usually squishy and keep to the backline, so Conviction @7 together with Subdue @13 allow to reach the much more easily and help you team secure the team. Only use this build if you have a divey team that can follow you up, otherwise you'll just find yourself alone behind the enemy lines and die. :(

Laning

Johanna is a very good solo-laner. With KtP you can clear waves really easily and your high survivability makes it easy to lane against most heroes. However, I recommend you lane conservatively - use only your W for clearing and E to harass the hero against you in the lane. You can use Q to clear more easily, but I suggest you save your mana and stick to AAs. Don't go pushing alone, since your damage is low and your tankiness is deceptive - being caught out of position can get you killed just like any hero, and since the early death timers have been increased you don't want that happening.

Team fights

As you enter a team fight with Johanna, you need to take a very different approach from what you might be used to from playing assassins. Your focus should be on one thought - what can I do to reduce the damage my teammates are taking? But lets break it down.
First in last out - You are the shield that guards the realm of men ;). Seriosuly though, you should always be the first to go in and the last to go out.
Positioning - You should always position yourself between your team and your enemies. Ideally, if you go back - so should they (true about the tank role in general).
Area Awareness & Peeling - Like all heroes, you should be constantly looking around you and assessing the situation. However, unlike assassins you shouldn't be looking for the enemy with the lowest health, you should looking for the most threatened teammate and see what you can do to save him. Did Illidan dive your backline? Blind him. Is Thrall running towards your support? Slow him or pull him back with condemn. This is your job - keeping your teammates alive by disrupting the enemy team.

General Tips & Tricks

• Your abilities do very little damage, so I suggest you think about them purely as utility. At least in the beginning, it will really help you to better grasp your role as Johanna. If you think of them as damaging abilities, you will try to pop them all together ASAP for burst damage (which doesn't work), but if you think of them as pure utility, you will only use them when they are needed.
• Use your "body" - even when all your abilities are on cooldown and you have no mana, you can use your body to absorb skill shots, block melees trying to reach your backline etc. Combined with Iron Skin, there's a lot of things you can do just with the right positioning and movmenet.
• Iron Skin is really good for a lot of things - you can use it to ignore nearly every CC in the game - you can use it to walk freely over the Garden Terror's polymorph, Malfurion's roots, Jaina's slow etc. Combined with the speed bonus on IS on level 16 or Condemn on level 7 you can chase down hard-to-chase hero such as Jaina or Lili easily.
• I often see people building Johanna for full survivability with all the Iron Shield talents (on 7, 13 and 16) etc., however you have to remember that survivability is only a means to an end - you need to live as long as possible in order to disrupt the enemy team and peel for your own team as much as possible. A Johanna that never dies but can't save her team is useless.
• Besides your basic abilities you have 2 big guns - Iron Skin and Blessed Shield. Usually, Iron Skin is popped during engaging, since this is when the enemy team throws everything they have at you and that's your way to just shake it off. However, see how your team fights unfold every game and maybe there's a better time to use it.
• Blessed Shield should be saved as an interrupt, since it's one of the longest range stuns in the game - you can use it to interrupt Mosh Pit, a Cup of a Thousand Jugs etc., so if you have someone in the enemy team with a heroic that needs to be interrupted, don't just burn your BS on engagement and save it for when you really need it.

As I promised, here are some vides of me Playing Johanna. Those were recorded while playing Team League with friends, so you can hear our comms and silly jokes :) I left the draft in the video since I really like watching drafts, but you are welcome to skip it.

Team League game on Battlefield of Eternity:
Play Video

Team League game on Infernal Shrines:
Play Video

Team League game on Sky Temple, also with TLV on our team:
Play Video

If there is just one thing I want the readers of this guide to remember from reading it, it�??s this: [TL;DR]
Johanna is a very specialized hero and therefore understanding WHAT she specializes in is key to playing her well.

This is all I had to say so far, thank you for reading this far. I'll try to get this guide updated with new patches and changes and I'll try to add more things that I will find useful. Also, this is my first ever guide, so I'd love to hear any feedback you might have. :)

Update 03/07/16: Added more builds, edited the text a bit, added videos.