There are a lot of awesome games on sale in the Because We May event going on this weekend, but of the titles I've picked up so far, League of Evil 2 is probably my favorite. It's a platformer title, in the vein of Super Meat Boy, in that it's basically a quick and simple romp through a series of quick levels. But while a lot of platformers don't work all that well on the iPad's touchscreen, League of Evil 2 works great. The virtual buttons are not only big and easy to hit, but they're very responsive, and great character and animation designs make it easy to move around the level quickly in very precise ways.
Each level is pretty quick to get through, but there are hidden briefcases