Marvel Nemesis, I really did enjoy the game to be honest, but it just wasn't quite there. The far out camera angles really diluted the action and the roster could of been a bit more expansive. Still the fighting was interesting and furious. Could have been so much more though. I'm just dying for a full 3D Marvel fighter I guess.
Tekken 6, big time. Solid engine, Tekken looking and running better than ever before with a massive roster of characters, but no actual game to play when you get down to it. Just Tekken Force basically.
Alien vs. Predator, the new one. Oh my days, I used to love AVP2 on the PC to no end and a current gen iteration of the series could of been epic. Wasted potential right there.
I could go on and on really, I also remember wishing that every moment of GTAIV wasn't boring as fuck. Also, that I'd never purchased it in the first place. Or the strategy guide.