The first impression I got from him was thinking of Kain: Defiance. If you know Kain, you'll see the similarities. This automatically puts him pretty high on my to-get list, although with the first week 7800 IP price I might just wait until his free week to test him out.
The name could be better, but ah well.
He looks viable top or jungle to me, and definitely gives off a melee ADC feel. I'm hoping the revive actually lasts about as long as Zilean's ult revive however - so that he can eat all the focus, then return while his team are taking care of enemies that all blew their skills on Aatrox. THEN you ult and start clearing up.
It's only a hunch I have, but I REALLY hope that Aatrox is the first champion to pull off Bloodthirster + Ravenous Hydra core. I'm talking dive 1v5 into enemy team, then hit Massacre and slaughter EVERYBODY while healing up with Lifesteal for all of their burst damage. Short of a knockback or other CC, if you can't keep him off you, he'll pentakill. And with his ranged E for poke and Q kept for disengage until the enemy team is weakened enough to slaughter them, I could see him being rather viable. But yes - the sheer factor he has Health costs puts him more on the bruiser scale than an assassin.
Imagine Morde with a gapcloser knock up. I just really like this champion, his abilities feel like they have synergy enough, though it IS all in the numbers. And Ignite should counter his passive quite well, plus it ought to build up slowly, I hope. But otherwise - like Katarina, powerful with/against the right team. Imagine Aatrox with Morgana's Black Shield to slaughter your team... although for that instance Tryndamere already works pretty well, heh. No reason not to carry them both for two Black Shield targets to bring along though.