The gist of Threes! is simple — swipe the screen to bring up number tiles, and keep swiping combine ones and twos to make threes, and combine pairs of numbers three and above to add them together into a single, higher value tile. Of course, every time you swipe you create more tiles, so you have to combine them just as fast, if not faster. That's because, if the screen fills up, your game is done.
Threes! is hooked into Game Center so you get leaderboards achievements and all the other trimmings. Mostly what you get, however, is good, clean, paid-up-front fun. And sadly, increasingly, that's priceless.
Threes! is perfectly conceived and brilliantly executed. It's what more indie games on the App Store should be. If you haven't tried it yet, but it now while it's on sale. If you have, tell me how you like it, and let me know your score so far!