Infinity Blade App
an on-rails ARPG by Epic Games, makers of the Unreal engine. There is not a whole lot of story as the game mainly relies on a self improvement mechanism. But the graphics are the best that has ever appeared on the iphone/iPad and the combat is surprisingly deep (without much frustration) and innovative. the amount of items available for purchase (with ingame currency) and level up customisation should satisfy a lot of rpg fans.
price includes both iphone and ipad version. Having played on both, I would have to stick with the iPhone, however. The graphics and resolution is more detailed and controls are far far easier as everything is within reach. Only downside is, if you're looking for all the secret pickups, they'll mostly be too small to be seen on the smaller screen.
game center integration, with multiplayer and lots of updates and expansions planned- this has plenty replayability. worth every dollar+highly recommended