Overview
It is the job of a support to mitigate your own teams mistakes and to punish enemies for their own. Introducing a support who takes a break from the more traditional healing role in order to more carefully sculpt the battlefield.
Feedback is a decent harassment tool and can be quite deadly against squishy mages - it is your primary offensive ability.
Obfuscate is a defensive ability which can be talented into several roles throughout the game including scouting, damage amplification and healing depending on the needs of the team. You can use it on yourself with 100% uptime if you want to stay cloaked, but it is better to save it for a team mate who might need the damage reduction and the escape.
Unstable Phasing is your crowd control. Unlike similar spells from other games (thinking decrepify from dota) units under the effects of unstable phasing can still attack. This minor change will allow you to use it defensively against auto attack heavy heroes (the butcher, illidan, kerrigan) while still being able to use it offensively combined with your own nukes and the followup nukes of your team.
Both of your ults have their place:
Mind Control allows you to have a much stronger lane presence, flipping entire pushes on their heads.
Maelstrom is a decent teamfight alternative to mind control. It's ease of use (instant cast time) should allow you to hit it more often than trickier, longer lasting stuns (mosh pit, devouring maw). It is most easily compared to divine storm, but has a shorter radius to make up for the ranged presence.
Early
Probably best used roaming between lanes or staying near a squish hero for extra protection from ganks.
Use obfuscate to curl around enemy positions and feedback to harass. Disengage often to allow your shield to recharge and perhaps switch lanes to find a better target. Use unstable phasing to secure kills with your feedback and to punish out of position heroes.
Midgame
Set up good team fights for your team - call a target, phase it and allow your team to wail on it with spell damage. Maelstrom 3 frontline heroes and jump on the back line with an obfuscated assassin.
Depending on your build at this point, you might be able to feed back for over 200% of a heroe's mana pool using Energy Backlash, Gathering Power and Strike from the shadows, combined with your unstable phasing and feedback, allowing you to fullfill a similar role to nova by picking single squishy heroes out before a fight starts.
If you went utility you can use Sight's Betrayal to scout which merc camps the enemy team are going for and coordinate ganks accordingly.
Finally, you could go protective shield and psionic infusion in order to shore up your teams defenses and keep them strong in skirmishes, similar to a malfurion.
If you took possession, don't forget to ult a creep wave before heading to an objective, the extra push will make sure the enemy pays for ignoring you.
Late
If you choose rewind you are capable of scary damage on your feedback. The combination of shield transfer and shield battery allow you to create a durable backline for your team and transfer your unnecessary shields up to the front where they are needed.
Alternately, aggressively position the battery and force enemies to make a choice between killing it or focusing your team mates.
If you have two charges of posession, the enemy illidan will be your best asset for 8 seconds straight, turning teamfights around.
Maelstrom with Psionic Vortex is a potent nuke and stun if you land it coming out of Strike from the Shadows. It is especially good for counter initiation as you can trap an entire team out of position (albeit for a shorter duration than a mosh pit or other similar skill)
I like the fact that he can pop in and out of lane like muradin, but the only thing he will be doing is auto attacking minions and using feedback on heroes. He doesn't have any wave clear.
I think I may have built a support nova...
EDIT: Also it appears that whenever I resize an icon to 30x30 I get a large raynor's passive icon. what gives?