Cranky Cat offers a new twist on the marble-shooting, bust-a-move genre, and it does it well.
Instead of firing spheres upward, they float in from the sides and slowly gravitate toward the center of the playing area. The player can (and has to) rotate the "board" to match the marbles. Three or more of the same color will remove them from the board, which then causes now loosened marbles to bounce off and gravitating back, which allows for quite spectacular and fireworks-like combinations.
There are numerous special marbles, such as the traditional bombs, and power-ups, like those that remove all marbles of a specific color. The game includes hundreds of levels in the story mode, and it also features a variety of endless/random modes, with the "lightning" mode perhaps being the most enjoyable one.
There are also Steam achievements and local highscores. The only feature I've been missing are Steam leaderboards, but this aside, this is a fairly enjoyable, fast-paced (at least deeper in the story mode and in Lightning) and smoothly running casual game (which can be quite hardcore). The developers have been very responsive to feature requests.
Worth checking out, especially at the very inexpensive super-budget price.