I love this guy. His playstyle is exactly what I want.
HOWEVER
His theme is supposed to be this dark hero who appears in the midst of battles to change the tide, however while he fills his allies with rage and strength, when he leaves they are left to be driven to madness because of the atrocities they have committed. So, to put that into terms of what he SHOULD do in game, he should be able to jump in, power up his teammates and then leave when the deed is done. But currently is the most boring and useless drain-tank in the game. His play style is supposed to be the quintessential drain tank. But he doesn't drain very well, and he doesn't tank very well, and he doesn't really do much of anything other than be unbelievably dominant if let to get ahead. From my person experience with him (and I have quite a lot), he really can spike very hard and win his lane and the game if he gets a first blood, and that point he will just out scale and out heal anyone who tries to fight him. By the time he's taken the first turret and probably gotten a kill or two he can start roaming and just shove lanes through until he's so strong he can fight most of team. With damage creep and the amounts of CC available on nearly any comp imaginable, he literally does nothing except sit there and farm and probably not die, but definitely not do anything helpful either.
They need to decide what he's gonna be. Is he going to be a drain tank who feeds off the enemies health, or is he going to be a support who jumps into fights and turns it around at a crucial time, but then disappears once the fight is over? Personally I would enjoy the first option more, but the second option delivers on his theme and story better.
His Q needs to be adjusted. Maybe a faster flight time and a larger radius? Or maybe make him invulnerable while flying in? I'm not quite sure what would be best, but something needs to be done.
His passive should do something to make him feed off the enemies. Some kind of draining. The revive is cool as hell and needs to be kept regardless. That's 100% a part of who Aatrox is. It's part of what clearly defines him as Aatrox. Ya kill him, and he just keeps coming back. However, the power up once his blood well is full doesn't feel right to me. I preferred when his passive gave him attack speed for hurting himself. That was pretty cool and actually very useful when used correctly.
His W is perfect I think. It's unique, not useless, and fits him very well. Definitely something else that needs to be kept in some fashion. More damage and more heals? Maybe, but that could get way out of hand. Maybe make it a little weaker to start, but it gets stronger as his blood well fills?
His E is pretty... boring. I mean it's interesting because it's the only skill shot in the game that narrows like that, but the slow isn't much. The damage is actually really good poke in lane, but it's hard as shit to land against any competent player. I don't really know what to do with it. It could get gutted and reworked or just buffed. I'm not quite sure.
But now let's explore what he could do as a support rather than a drain tank.
I think right from the start, as a support, he would be an initiator and a healer. Rather than his healing be direct like Raka or Sona, it would be more of stealing the enemy teams health. He wouldn't be the best at either, but he would be good at both.
So his Q would definitely stay. It would be a stunning way to enter a team fight, and is great for catching out of place targets, escaping, or initiating. If he was a initiator type of support, he would need some way to really get in, because against any competent team they can just CC him out of the air and now it's on a long ass CD.
His W would probably stay as well, but have some way of assisting his team mates. Maybe a certain percentage of health stolen from enemy champions would be returned to his lane mate or whoever his closest to him? That could be super OP in lane and then might not benefit that much in team fights as he would probably just be healing any other thanks or initiators, but then again he could be healing up melee fighters or assassins. So I'm not sure how they could get balanced out, but something like that would be interesting. The damage option could just stay the same, but use his health to deal the extra damage.
His E could actually stay the same as a support, or it could be reworked into something entirely different. I was thinking maybe some kind of steroid for his lane mate, but I think that would fit better on his ult. Maybe something like it slows enemies, but if it runs through an ally it speeds them up? Not a huge boost because that would be crazy, but a small boost like 10-20% or something might be nice. I don't know how or if that could be balanced, but it's food for thought.
His ultimate should definitely have the AoE damage, and probably give any allies caught in the AoE extra attack speed and maybe life steal for a short duration (somewhere between 3-5 seconds would probably work best), and the more his blood well is full, the more damage it will do and/or the more potent the steroids are.
His passive is where I feel changing him to a support would get the trickiest. If he is a support, should he be able to revive still? It would nice and gimmicky, but at that same time it could get quite overcrowding if you have this support who you have to kill twice. His revive is conditional right now, which is good. It should be conditional, it shouldn't be literally every life, that would be stupid, but how could you balance a self revive on a support? Zilean can give a teammate a GA for a short time, and the timing is what balances it out, but what do you do when this tanky initiator dies, and then comes back, and continues to keep draining health from your team? I really don't know what you would or could do there. The blood well can be a good thing for a support. He could have the ability to drain it and give it to his allies, but make it harder to fill up. You could make it have a choice to it as well, if its full he could give the health to a teammate, or he can use it empower his abilities and thus give greater boosts to his allies. OR you could make it very binary, and go one way or the other. This could also help balance the revive. If he uses his blood well, he can't revive. So there he has three choices on it now. He could heal an ally, revive himself, or boost his allies. That would be cool and unique.
Overall he's in some serious need and Riot needs to decide what they want to do with him and who they want him to be.