The popular new game on the App Store at the moment is Threes!. It looks sort of like a sliding number puzzle, but the concept is completely different. The idea is, starting with a 1 tile and a 2 tile, you match tiles together to form ever-increasing multiples of three.
The catch is, a tile can only pair with a matching tile (except 1 and 2), there are only 16 spaces on the board, and every time you make a move, a new tile is added. The game is over when no more tiles can move.
So, should you buy it?