Domino Drop is one of the iOS games I'm playing these days, and I've got to say I just love it. It's both adorable and challenging, two qualities I love in a game.
It reminds me of Tetris; the blocks drop down from the top of the screen, and you try to match similar colors to both get points and make blocks disappear. When the screen is full the the game is over.
Other than just the gameplay (which is very fun!), I really love the music in this game. It reminds me a lot of the music in Flight Control. Calm and cheerful, it makes the play experience that much better. Just watch the trailer, you'll see what I'm talking about.