Angry Birds Lite is an addictive physics-based puzzler with a lot of personality. It's so easy to pick up and play, it's hard not to recommend this game to every new iOS device owner.
You're helping a bunch of birds as they wreak vengeance upon a crew of smug little egg-stealing pigs. Basically a one-player, turn-based artillery game, Angry Birds has a dead-simple interface: you just pull back on a slingshot to launch birds one at a time, with your finger position determining the speed and trajectory of each bird. The only other interaction comes when new birds (essentially, different ammo types) are introduced: a tiny, MIRV-like bluebird and a speedy yellow bunker-buster, whose special abilities you activate with a single in-flight tap.
On each level, you have to use a limited number of birds to wipe out all the pigs, who are taking cover in a series of architecturally questionable structures. These precarious forts are built with ice, wood, and rock, all of which react differently to your incoming bird projectiles, and much of the game's challenge is in figuring out their weak points--so you can use the pigs' own buildings to crush them, or to leave them exposed for future shots. You can increase your score by using fewer shots (that is, birds).
In addition to a satisfyingly simple interface, Angry Birds has smart level design (tough at times, but not impossible), achievements and leaderboards through Crystal, and an instantly endearing visual and audio aesthetic (the birds' constant, goblinoid gibbering is one of the best things about this game). If you're a fan of pick-up-and-play arcade puzzlers, Angry Birds Lite is definitely worth a download.