It's hard to overstate just how good <em>Threes</em> really is. Touch Arcade's review deemed it a "perfect mobile game." Ken Wong, the lead designer of the Escherian insta-classic <em>Monument Valley</em> said that <em>Threes</em>, ostensibly a rival for mobile mindshare, was "one of the most elegantly designed games since Tetris." Indeed, its central mechanic--sliding like-numbered tiles together to create higher-numbered tiles--is so utterly simple and exquisitely satisfying it seems like the type of thing that doesn't get invented so much as discovered.