Yosumin! is a fun take on the "find rectangles" type of puzzle game. The game is pretty, and the gameplay is pretty basic but solid. There is a bare story which justifies some of the goals in the game in a way that doesn't seem completely arbitrary: A stained glass window has been broken and the pieces scattered by somebody bad, and your job is to go find the pieces and bring them back.
The puzzle game has players making rectangles by selecting Yosumin! of the same color; the color of the Yosumin! inside is irrelevant, so that large parts of the board can be cleared at once. The game features a variety of goals, which adds spice to the game by requiring you to make groups of certain sizes, shapes, or colors. There is also a meter which fills up and will clear all the Yosumin! of a particular color from the board, which adds additional variety to the game.
The appearance of the game was also pleasing, in a simple minimalistic way. The shapes were distinct and colorful, and the backgrounds were dandy. It seems unlikely that Yosumin! will be taxing anyone's graphics card, if they bought there computer more recently than 1999.
There wasn't much bad to say about this game. The gameplay might get a bit repetitive, as it did for me after an hour of play. I doubt there's too many hours of gameplay, but that's a speculative judgement. The game's simplicity may become a burden in the long run, but I think this game is fun enough to be considered worth playing.