Kaleidoscope Reef is a simple, but relaxing, game. It's neither a complicated game nor a long game, but it's a clever enough concept to provide some fun action.
So, the basic concept is quite simple. An evil ship has caused your beautiful reef to become polluted. In order to restore it, you have to plant new polyps, and then feed them by dragging plankton to them to get them to bloom into beautiful new coral. Once you've restored enough of the reef, the game proceeds to a new section, until eventually you've eliminated the pollution and restored the whole reef. At the beginning, your polyps are omnivorous, but as the game progresses, you'll need to feed them the correct-colored plankton (and getting the correct plankton is not always easy, either). The environment isn't always friendly, either -- as your reef blooms, fish of all sorts will be attracted; some just look pretty, but others can hamper your progress by eating things that you'd rather remain uneaten. The pollution can also pose a hazard to your burgeoning reef, as well.
That's pretty much all there is to the game. Like I said, it's a simple game. The graphics are vibrant and a bit cartoony, but overall the game is quite pretty. The music and sound are both quiet and peaceful; the music does a good job alternating between different melodies, so you don't get too bored, and in any case, it's unobtrusive enough that it never is particularly annoying.
As far as I can tell, you can't really lose the game -- while you get bonus points for the speed with which you complete the level, there's no actual time limit, so you can take as long as you want. So this is really more of a relaxing, peaceful game than a challenging game. Still, it's a nice change of pace and a game you should find entertaining.