RPG:
- Pokemon: Regardless of all the hatetards it's still got an incredible amount of depth and even more in terms of content and playtime than even console RPGs.
- Nostalgia: Battle mechanics are pretty textbook outside of aerial battles but it does them very well.
- Sands of Destruction: Fun game, not much else to say outside of that.
- Tales of Innocence: A great translation really helps here, and the battle system, graphics, and even the story are good.
- Final Fantasy IV: Although this is a shitty version of it, if you don't have another way to play it (like the better GBA version), this is acceptable. It's a FF game worth playing.
- Puzzle Quest: CotW: The PSP version is a lot better, but this is fine. There's a lot to do and I love the Bejeweled battle system. The original is better than Galatrix or the sequel.
Fighting:
- Jump! Ultimate Stars: Even if you don't like manga (like me), it's still the closest to SSB you'll get on the DS.
Not sure what else here, people say the Bleach games are decent fighters, but I haven't bothered.
Racing:
- Sideswiped: Beats Mario Kart DS in my book any day. It's an awesome Burnout-like game. Balls to the wall speed, crashes, explosions, and it gets pretty varied too. Only thing that sucks is no Wi-Fi competitive modes outside of leaderboards, but it's awesome.
- Mario Kart DS: It's still a good kart racer though, and probably the best reason to do Wi-Fi on the DS.
- Sonic and Sega All Stars Racing: Only problem with this is handcramps from using all the face buttons + bumpers, but it's still fun enough.
- Speed Racer: One of the better movie tie-in games there. Kinda like F-Zero with some interesting mechanics. Fun game.