Buyers beware: This is an extremely good game!
This game is amazing. While you may be looking at screenshots and thinking "Ugh, another Tetris clone. I'll just wait until Tetris DS comes out and get that instead." you are totally wrong! This is not a Tetris clone... the only thing very similar is the fact that blocks fall from the top of the screen to the bottom of the screen.
The main goal is to group Meteos (the blocks) into groups of threes. This may seem easy, but, unlike Tetris, you can't move blocks before they fall down: they are meteors, they move on their own schedule! The only way you can move them is vertically and horizontally once they've landed. This makes it somewhat harder to align them.
This game is very fast paced, and it can be even faster if you turn up the speed controls. It can get very hectic while playing, as the Meteos move faster and faster, plus all the Meteos that your opponents launch (send back up to the top by grouping them in groups of 3 or more) are sent onto your screen, or another opponent's. This adds to a difficult element in the gameplay, as it is hard to get them all off in time, without having them all stack up to the top.
When you start a game you usually get to choose what planet you start on. The planets are very different from one another. Each planet has different Meteos that fall, and you'll want to collect each kind (you gain every Meteo you successfully launch) in order to unlock other things, such as other planets, sounds, and other extras. Each planet also has different gravity levels and bonuses, such as one allowing for no vertical launches but very fast horizontal (groups of three across, no groups of three up and down) launches. On some planets the Meteos fly down very quickly, as well as rise quickly, but on others they fall down slowly and rise slowly, sometimes requiring multiple launches in air in order to send them up.
This game has many modes, a "play until you die" mode, where you play until...you die :). Another one is a time attack, "stock" attack, where you play until you die a certain amount of times (or your opponent dies first), and last but definately not least is the story mode. Each mode can be played for a few minutes or many hours, depending on how much time you want to play... however, this game can take over your life! It is a highly addictive game.
When I first picked it up, I didn't really like it, and was mad because it got such great reviews. I kept telling myself "Ok, I'm shutting it off in a few minutes and going back to Mario Kart." The next thing I know, it is 3 hours later! It is a highly addictive game with so many modes to give you amazing replay value, as well as TONS of unlockables.
This game will last even the most hardcore DS gamer MANY hours of play... I doubt you will get bored of this game for a very long time. I'm not normally one for puzzle games, but I love this game. I recommend anyone with a DS to pick this game up, as it is one of the best DS games out now.