Katamari Damacy. It has a reputation for being silly Japanese nonsense, but the gameplay is brilliant, the graphics are timeless, the soundtrack is incredible, and it has some surprising thematic depth.

Annoyingly, it initially seemed to work well on my iPad (only lacking right-click support, which upped the difficulty nicely), but now it only shows the multicolored loading screen forever. Not a cookie thing either, since it does the same thing in a private tab.