Some thoughts and tips about abilities:

Dive (Q)

Dive has a 6 sec CD and is a very good gap closer. Not only that but you are also able to use it effectively to get in or out of combat and even go over walls/buildings to chase/escape. More over, you're able to evade non-instant stunts (like golem's pound or uther's Hammer of Justice and even Tyrael's stun ult) by being mid-air during the dive. You still take the damage but you negate the cc part (works with valla's tumble as well). It's even worked for escaping Zeratul's Void Prison as well.
Play Video
It doesn't do very much damage, however, and interrupts your normal AA attacks, so I wouldn't use it during combat, not to mention that you've also likely lost one of two chasing abilities.


Sweeping Strike(W)

Sweeping Strike has an 8 second cooldown and boosts your AA damage by 35% (or 50% if you choose the talent). It deals a good amount of ability damage itself and should be used in normal AA rotation if possible, but don't use it if you're likely to overshoot your target and allow them a chance to escape, use it only if you feel the enemy is committing onto you.



Evasion (E)

Evasion has a 15 second cooldown and causes all auto attacks to miss for 2 seconds. I consider it one of the most overrated abilities in game, but due not to its actual ability. 15 second for a 2 second miss is pretty insubstantial. I must admit, I've been saved by this ability at times, but for a 15 second CD ability, it's just not worth having it take up an ability slot. Sure your passive reduces its CD, but even then it's still an ability with a very long CD that doesn't perform enough.



Betrayer's thirst (passive)

A very top tier passive that has two parts: a lifesteal of 20% and a CD of ALL abilities by 1sec per AA. This is like having a buffed Vampiric Assault talent and buffed Battle Momentum talent built into one.

Metamorphosis
Regeneration Master is a highly underrated talent that really should be the staple of any survival Illidan build. You should not be sitting in one lane if you are using this talent but should rather alert your team at the beginning of the game to not grab orbs in lane and save them for when you get there. Roam as much as you can and just focus on killing the mage then going away, unless you wish a gank. By lvl 10, you should be regenerating at least 1% of your max hp per second. By late game you should be regenerating at more than 1.5% per second.

Don't take Evasion Shield
I consider evasion shield to be useless as it essentially replaces your missing evasion trait into a 10% max health shield. It's not that you lose your miss element, but it's that miss mechanics bypass shields, meaning that despite having an attack miss you, your shield takes damage, thus reducing the effectiveness of it. For those who say that they've been saved by the evasion shield by taking spells is reducing every application of evasion to be the most ideal case which is a poor excuse to take this talent. Just don't.



Hunt
Seasoned Marksman is pretty good for a hunt build which emphasises as much damage in as little time as possible. But the farming mechanic required means you must stay in lane. Get battered assault if you prefer ganking or do not want to farm.

Metamorphosis
I've gone back to thirsting blade. Marked for death seems to be a little weaker. As with Illidan's general gameplay, it's best to avoid team fights where you're outnumbered or underlevelled.


Hunt
Marked for death is generally not something you use during a consistent fight. It is really more for quickly killing those fleeing or diving under forts when your attack and move speed become slowed. Immolation isn't as good as it generally only does roughly the same as an enhanced AA but over 4 seconds.


Also, fel reach is largely useless.

Metamorphosis/Hunt
An essential skill for Illidan who is so squishy yet lacking burst. You should pop this early, before having taken a full 35% damage as it will continuously heal you even if you were to heal up to full and then take damage. Healing it after taking 35% may sometimes be too late as bursts can really kill you.

Every other talent pales in comparison to first aid so I don't consider them.

Metamorphosis
Illidan's iconic form. A 20% temporary bonus attack speed boost may seem lackluster, but when you're able to slam into a 5 man team then pop your first aid for 35% of your new max hp, it is very formidable. It deals a decent amount of damage but the greatest trait of this ultimate is that it makes you invulnerable/untargetable for around 2 seconds, which you can evade around 2 or all of Nova's triple tap as well as her ulti and any other lock on abilities. The bonus AS also syncs very well with your passive.

You can also use this to jump over walls and escape.



Hunt
Hunt can also be used as an escape by targetting an enemy (minion or otherwise) in a different lane than one where you're being ganked at. It provides a 1 second stun on impact which can also help a team if a channeled ability is being used (e.g. strafe by valla or triple tap by nova). It also does a fair bit of damage which also helps with the damage build.

Metamorphosis
This ability allows you to 1v1 warriors now. If you don't get this ability, you should always lose to an arthas, sonya, chen... etc(not the champ but et cetera). You have a quick AA which makes this giant killer deal damage quickly as a bonus to your normal AA damage. But this is a spell-type damage so you don't get healing bonuses from it. Another reason why this is a superior skill is by thinking of it this way. If you land in 10 hits, your opponent has 15% less hp as well as whatever normal damage you do, however by not taking this skill your opponent has an extra 15% hp.

The other abilities pale in comparison to this skill except unbound, however, since they are competing in the same talent space, unbound is poorer.

I believe Sixth Sense to be a poor choice for the same reasons as evasion shield. It forces you to choose between two mitigations most of the time and it's also a case of most idealistic situation where you take only 50% of spells while AAs are missing you. If you're taking spell damage, it's likely you're CC'd anyway.

Hunt
You should also get this for the hunt build as you'll be doing more damage, and damage is what you want.

Metamorphosis
I pick this ability over Blood for Blood for two reasons:
1. It syncs very well with your metamorphosis. After slamming a team of 5, you now have 65% extra health of your new max hp, when combined with first aid, and 30% of your default hp is most likely more hp than you would get than if you were to cast blood for blood on any warrior.

2. It is non-reliant on hitting a target. So if you get tagged with double bombs by an invis zeratul or locked on by a nova's triple tap, this allows you to most likely survive the barrages. Also Blood for Blood heals for 15% of whatever you hit, so if you happened to target another assassin or some low hp target, then your heal value is much lesser.



Hunt
Blood for blood deals damage and damage is what you want. Also the enemy gets slowed which helps with saving your abilities for more chasing or outright damage.

Metamorphosis
This makes your ulti permanent and allows you to save your ulti for escapes or general healing/damage. It also increases your AS to 30% and reduces CC by 50%, which greatly increases your ability to survive. This also syncs well with your passive as you get CDs faster and heal more.

Hunt
Allows you hunt from anywhere, even from your spawn to their core. You might be able to backdoor if core health permits and enemy team is distracted.



Bolt of the storm isn't bad either, but I feel that improved ultis are better. Taking either one should be fine. Fury of the storm doesn't do enough though, and I'm quite sure that the splash does not heal you.

Overall, farm orbs otherwise you'll have wasted your lvl 1 talent, but if you farm well, you can essentially 1v2 a lot of the times when you get past lvl 13.

Do not just randomly dive or sweeping strike an opponent as you'll put your chase abilities on cd. AAing and just evading should be enough to out-sustain your opponent into having to run away, which then allows you to get free shots on them for more damage and healing. Use sweeping strikes only to catch up or when you know the enemy is committing on you.

Early Game- Most of the time, don't try to fight the enemy head on. Best tactic is to q, get one or two hits in, then w away and wait for CDs. Most enemies flee once dove on so you get lots of free damage that adds up over time.

Mid Game(Meta only)- With these talents you are a great jungler. Jungles also give regen orbs which help with your talent and also helps push your lanes. You should also come out with 100% health which means you can immediately lane or go gank a lane. A tip for knights is to kill the mage first then focus one of the knights, while dancing around so the third knight spends most of its timing chasing you. Pop evasion whenever it's up and don't forget to w.

Late Game- Stick with your team, laning becomes a lot less important once death timers become longer. If you're able to kill most/all of the enemy, you can push a single lane for the third tier and even core occassionally. You can also solo a core largely due to your evasion passive as well as bonus healing/defense with passives and talents.

Lastly, I find this to be a weaker build on Haunted Mines map as regen orbs are hard to come by as well as the mines being a terrible place to farm orbs unless you're able to get the golem fully.