I know a few people who've been contemplating buying a Nintendo DS, but haven't done so. I've never used a PSP or a Gizmondo, but I think I can say with a good degree of certainty that the Nintendo DS is the best handheld platform out there. It's selling better than the PS3, XBox 360 and even the Wii. So for those looking into a DS, here is what I believe are the best games on the system.
In my opinion, the DS's best game is The Legend of Zelda: Phantom Hourglass. I'm playing it right now, and it's phoenomenal. I was going to write a review, but Brandon has recently written one, and his review is far better than the one I'd write, so I'll just link to his. Let me just say that I'm enjoying the game thoroughly, and that if you're playing you should send me your friend code so that we can trade ship parts and treasures.
Next up, Mario Kart DS. I've never been a fan of racing games, but in between everything else I play, I keep coming back to Kart DS. It's just fun. Great game - until Zelda I'd have said it was the best game on the system.
Puzzle Quest is a game I've previously reviewed. It just came out for $15 on Xbox Live Arcade last week, and I've been trying to persuade my brother Sean into getting a copy. It's just a lot of fun.
Both Brain Age games are also really good. They've got Sudoku in there, which never gets old, and while the first one has better training exercises, the second one has Dr. Mario. I've scored over 1000 points and gotten up to level 13. Beat that!
Elite Beat Agents might at first seem odd, but it's another great game and makes fantastic use of licensed music. When I first heard the level set to the song Napoleon Dynamite dances to, I was groovin'.
Advance Wars is a great little Turn-Based Strategy game, and suits the DS perfectly. I still haven't finished playing, but I'll keep going back until I do, and when the next Advance Wars comes out, I'm all over it.
Lastly, Phoenix Wright. It's an adventure game and involves more reading and story than gameplay at some points, which could put many people off, but it's great for air travel - I played most of it over the Atlantic last year.
You might also find people who argue for New Super Mario Brothers, Meteos, Mario and Luigi: Partners in Time, and Castlevania: Dawn of Sorrow. I've played three of those four, and they're good, but not amongst my favorites. Still, this should give new DS owners a jumping-off point for game purchases.
One of these days I'll get a DS of my own. I agree with you in that it's the best handheld platform out there, at least as far as quality of games goes. I play my PSP pretty much every day at lunch and graphically it kills the DS. There just aren't very many quality games for it right now.