Hercules - Curse of the Hydra isn't exactly the most polished game I've seen on the iPhone -- it's a little clumsy, in fact, with some awkwardly placed controls and graphics that aren't quite as smooth as they could be. But it's still an interesting title and a solid effort from an indie studio, and I like its ambitious nature. There are 16 different levels of platforming and 3D action to fight through here, and while the game is still a little rough, it's cool to see a small studio take on a full title like this on iOS.
Unfortunately, there's no Game Center integration, but there's a nice progression scheme to explore, which should keep you charging through the action and the storyline. There's a free version of the game to try out (and I actually recommend you give it a shot before you buy the full game, just to see if it's your thing). The full version is US$3.99 on the App Store right now, and I think it's worth supporting this studio, called Smerc. There are a lot of little pick-up-and-play puzzle games out on the store, but I like to see someone trying to tackle an experience that's a little bigger than that.