The basic mechanic in the game is to launch a colored pill from the bottom of the screen towards the top. If you manage to hit like-colored pills, those pills match and fall of the screen. You continue this process until you clear the board.
The level structure of the game is also interesting in that it offers some varied gameplay from level to level. Each level carries a different arrangement of pills (circular or horizontal) as well as different uses for the accelerometer. In some levels, the accelerometer controls the aim of your launching pill while in other levels, you control the movement of the other pills. There are 10 levels in all which are played in sequential fashion. Each level is "solved" once you clear the board. The levels do get progressively harder as you progress.
This discrete level progression is unlike most puzzle games and results in a somewhat unsatisfying feeling when the game simply ends after level 10. But local high scores are kept and the speed at which you complete the game increases your score giving you an incentive to try again.
The developer's gameplay video shows some different levels. Note the music does not play during the game itself, just in the title screen.
Overall, a fun game that I ended up spending more time playing then I had intended. In some ways, the game reminds me of Snood and manages to feels right at home on the iPhone.
App Store Link: Popper!, $1.99