The puzzle aspect of the game is similar to Tetris, but the author has added several clever twists to make it into a more compelling multiplayer game. Multiplayer mode, also know as death match mode, calls on yout to last as long as possible. You defeat you enemies by dropping extra block on them. You drop extra blocks on them by clearing two or more lines at a time. You also have the use of various powerups (both attacking and defensive).
The AI is reasonably good and it will probably take a you a few tries before you can defeat it (they start dropping blocks on you very quickly). As the author puts it 'consequently, the multiplayer game can still be enjoyed even if you have no friends with Series 60 devices or indeed no friends'.
The game is even more fun when played against another human who in general tend to be a lit bit less relentless that the AI. I would recommend keeping a copy of the SIS file on your memory card so you can send it over Bluetooth to your S60 phone owning friends.
The author has also put together a comprehensive website, which is well worth a look.