While I initially kinda bagged on Epic for their iPhone Unreal preview, I have to admit the game Infinity Blade by Chair Entertainment Group is quite a bit of fun. It's got the right mix of gameplay for a mobile, combine with a high production value. Part of the reason I disliked the PSP when it came out is that a bunch of Playstation developers simply ported their console games to the mobile space, complete with long cutscenes, and expectations that a play session would last a while. Infinity Blade still keeps that easy to pick up and put down aspect that I want when gaming on a portable device.

Bonus points for also making it a universal app, so one price to have it on both my iPhone and iPad. Now what they really need is to also have a way to sync back and forth. Maybe GameCenter in iOS 5 will add something like SteamCloud for cross device game saves. Rovio mentioned working on something similar for Angry Birds, but nothing yet.