The unit itself works great. The screen is very easy to see with the backlighting, and the touch screen also works well, and I rarely have problems executing even the most precise actions using the stylus. I must admit, when I heard that the replacement of the Game Boy would have two screens, one of them a touch screen, I thought it was a pretty stupid idea. But the system really is ingeneously designed, and allows lots of very innovative styles of game play. And at $129, it seems like a pretty good bargain. I really have no complaints; sometimes the small size of the unit makes long-term play uncomfortable, especially for games that utilize the standard controls rather than the touch screen. And even the more compact Lite unit won't fit easily in any but the largest pockets. But still, it's a great system, especially with the innovative games being made for it.
I picked up a fair number of games when I got the system, and found them all to have some merit. The game I play the most is probably Brain Age. This is a sort of mind-teaser game, which is based on a series of best-selling self-help books in Japan. Basically, the game quizzes you to determine the age of your brain, and then gives you brief exercises, mostly basic math or memorization, along with reading aloud, which will exercise your prefrontal cortex. It's the sort of thing that's perfect for the DS. The touch screen and microphone (for voice recognition) allow for lots of different simple exercises, as well as a bonus Sudoku feature (the best way I've ever seen to play Sudoku), and the game actively encourages you to play in very brief sessions, which is what you want with a portable game system. When you first start, it is actually frustrating how few features are unlocked. You get more exercises as you go along, but still, even after unlocking all the exercises, I could do them all easily in about ten minutes. But since you're encouraged to revisit the exercises every day, the replay value of the game is enormous. The handwriting recognition works very well for numbers, though it isn't completely perfect. Recognizing letters (which only comes up in one test) is more problematic, and the voice recognition is only so-so (it has a hell of a time recognizing the number eight when I say it--I had to resort to substituting "eat" instead, as that seems to work). But still, for $20 (cheaper at Costco), it's a fun game, and the sudoku as an added bonus makes it an even better value.
I also got Big Brain Academy, which is similar to Brain Age, in that it also has tests to measure your brain (weight instead of age, in this case), and various mind-teasers to exercise various aspects of your brain. Comparing it with Brain Age shows something curious: Big Brain Academy has a great deal more variety, with tests that are more complex and interesting, yet Brain Age is easily the superior game. The austerity of Brain Age, and the simplicity of the exercises, helps to give some degree of credence to its claim to be a self-help product. Big Brain Academy doesn't really claim to be a scientifically-rigorous psychological tool, but just a series of games, and the games really aren't that much fun. Like Brain Age, they're over quickly, but still I have the feeling of "Thank God that's over" far more often while playing Big Brain Academy. It's still a decent game for a bargain price, but Brain Age is definately the more engaging of the two.
New Super Mario Bros. is also a pretty cool game. Not too hard to beat, but there's still a lot to go back and discover (I finished the game and never made it to two levels). The best parts are the things that are most faithful to the original Super Mario Bros. Some of the more novel additions, like the mega mushroom which makes Mario huge, or the micro mushroom that shrinks him down, are fun the first time or two, but the novelty wears off quickly. Despite being a new game, nostalgia is what makes this game interesting, but that's fine. It's very well-implemented.
Those are the games I've played the most. I also enjoyed Trama Center: Under the Knife. The touch screen creates some great opportunities for game play in this surgery simulation game. But it's a very difficult game, and can get frustrating. Meteos is a pretty fun puzzle game, though it didn't quite live up to the great things I'd heard about it. Seems like luck comes into play a bit much, but maybe that's because I'm still learning about some of the more subtle aspects of the game. Bust-a-Move DS was a bit of a disappointment, but I have a feeling I might come back to it once I get bored with the games I play more often. And Metroid: Prime Hunters seems fun, but I just can't get the hang of the controls.
Perhaps one month isn't enough time to say for sure that the Nintendo DS was worth purchasing. But so far, I've gotten quite a bit of use out of it, and found some very good games to complement it. I was sceptical of the DS when it was first announced, but now I'm a believer.