Alien Swarm is FREE! (4.99 > FREE)
Given the recent notice of Galaga/Galaxian iOS games with the Namco 30th Anniversary release, this is a particularly nice freebie pickup for those who don't have it or haven't jumped on the new Namco/Bandai offering but love vertical shooting retro goodness. Just different enough to be its own game, but close enough to the originals that it'll hit that arcade sweet spot for anyone who needs a fix. Rated highly, and richly deserves it.