Like so many of the things installed on your iPhone, Threes! is a game of pattern-matching. A one and a two make a three. Threes and up can be matched only with identical tiles. 'Swipe to combine tiles' is all the instruction you really need to get started, and indeed the game offers little more than that as you complete its wonderfully light-touch tutorial sequence. Of course, by then it's too late. It's much too late.