Don't expect a lot of variety here. >_>
Tetris DS... um... first let's start with one of the most essential modes, and the one that everyone plays first.
Marathon mode. I don't know who specifically designed this game, but there is something essential they must know. IF YOU ARE USING WORLDS ROTATION YOU MUST HAVE A TIMER. There is none in thsi game, and instead, you have a makeshift "score attack" mode. While this may seem good at first, it is very flawed. You'd think that to get a high score, you should only get Tetrises, right? Well, guess what. Doing T-Spin Doubles for the entire game will give you an even higher score. Sucks for you if you don't know what that is, because I don't remember seeing T-Spins explained anywhere in the game or in the manual. Way to go, Nintendo.
Next we have "endless" mode. If you can clear the normal Marathon then it doesn't take much more effort to play this, because remember, we're using WORLDS rotation, meaning that any idiot can keep rotating a piece all day long while trying to figure out where to place it. So, what's the point of Endless mode then? Get to the highest score, 99,999,999? Too bad that it takes several hours of nonstop play to reach that, and if you go one point above, the score won't save.
"What about Line Clear mode? That's gotta be better, right?"
This video, and the comments with it, are self explanatory.
Short answer: No.
Next we come to VS mode, which is one of the few modes in the game that is actually good. Mainly because of the fact that hard drop only takes one frame, making for a fast game. But not fast enough, because line clear animations in this mode are still annoyingly long, and holding left or right so the piece moves faster? Sorry, but that is just pathetic. Not too slow to be useful but come on. It was faster in freaking Tetris DX.
Unfortunately, VS mode is still flawed mainly because of garbage. Far too often, one player will get "clean" garbage where the holes are all lined up perfectly, and the other player will get "dirty" garbage where the holes are all over the place. This is just stupid. T-Spins (again, what are those?) help but not by much, when you still have to deal with 5 or 6 horribly slow line clear animations to get to that clean garbage while your opponent doesn't have to deal with any.
Oh, and we can't forget VS mode with items. If you like "party" games, then here is Party Tetris for you. I prefer to stay away from it.
Next we have Push mode. This mode is nothing new, regardless, this is where almost everyone got to play it for the first time. It's fun, but I don't play it often, and you're about to see why.
Puzzle mode? Uh, sorry, no. This got old quickly.
Mission mode is okay. Just okay. It could've been done a lot better. If you want to see a Mission mode done correctly, get TGM ACE. (That is, if you're willing to import a Japanese 360 and crap...)
Catch? Tower? I'm sorry, I wanted to play Tetris. What the heck is this crap?
Now that we have everything else out of the way, we can go ONLINE. Whee! Online, there are three modes, but only one rating. WHERE IS THE LOGIC BEHIND THIS? Did Nintendo not think that a player could be skilled in Standard mode but not Push, and vice versa? And don't get me started with 4P w/ Items. That's just rating suicide. Never mind the fact that 4P matches take forever to get started, and can easily end before they should, because for some reason, you must have all 4 people to play.
Oh, and here's another reason why the rating system is flawed. One match will decide the winner. That's like doing only one race in Martio Kart. It just does not work. VS matches aren't even that long, so there could've easily been 2 out of 3 matches, or even 4 out of 7 matches. But no, one match and that's it. One player could make a rare mistake and the inferior opponent will run away with a higher rating.
Well, that's it, I'm done. In short, for a competetive Tetris speed-freak, Tetris DS is good for one thing only. Online VS. Considering how excited Nintendo is about their "new modes of play", this isn't a good thing.
Final rating: 6.5
I'll do Terranigma sometime later.