Ohgod here I go
This is for everyone since I look these up sometimes myself.
Puzzle RPGs**Ghost Trick: unique puzzle game, awesome storyline. Pretty short, and you could finish in a few hours with a walkthrough (so don't) Not much replay value
Trace Memory: Okay puzzle game, decent storyline. Very short, little to no replay value
**Professor Layton: Puzzle game with hundreds of puzzles/riddles cumulatively. Pretty fun for brainteasers or to get unique ideas. All of them have cute storylines and the last two are really sad. 3 games are out so far (I think 3 more coming, and a movie was released)
Phoenix Wright: Puzzle/investigation game. Cool series, some people like it more than others. Pretty long story, so it'll take a while to beat each game.
999: Like an online point-and-click game. I only played a few minutes of it, MOST OF WHICH WAS WORDS, which was highly boring. Buuut it looks cool I guess? They don't utilize the fact that it's a videogame very well, and narrate every little thing...
Strategy RPGshaven't played many of these since I suck at them ono
**Pokemon Explorers of Sky: omg get this. As far as strategy goes it's pretty easy. Mission-based dungeon-crawler WITH POKEMON, with an awesome storyline. Awesomeeeee. Lots of replay value and hours of gameplay, as most Pokemon games.
Disgaea: I haven't played much of these because it's too hard for me haha. So yeah.
Shin Megami Tensei - Devil's Survivor: By the creators of Persona with similar aspects. Story about the world ending and you having to stop it. It's... pretty hard though xD But fun.
Final Fantasy Tactics A2: idk it looks cool. I forget if this is the only tactics game for DS, but I don't think it is...
Action RPGsPhantasy Star Zero: Couldn't manage to beat the boss, so I don't know how good the story is, but it's basically like an online MMORPG for your DS
(without as many people)
Avalon Code: Fun if you like games where you get to collect things on the side. Story is decent, I guess. It's pretty easy though since you can customize a lot of the world, making monsters really weak or making your weapons invincible.
**The World Ends With You: Highly recommended! Great story hours of gameplay. Tons of unlockable secrets and lots of stuff to collect.
Zelda- Phantom Hourglass: Really short for a Zelda game, but still pretty fun.
Kingdom Hearts 358/2 Days: Good if you've played the original KH games since you'll get the storyline and references. Like those, it's a button-mashing smash-em-up game where you play as the antagonists from KH2, the only difference is it's mission-based so you have a bit less freedom. But you can play multiplayer, which is fun as long as everyone's on the same level.
Final Fantasy Crystal Chronicles: idk it looks cool. haven't played tho.
Okamiden: not out yet but it looks cool haha.
Rhythm games**Taiko no Tatsujin DS: Epic funnnnn look it up on youtube. However, these are JP only so you'd need to order them from Japan or get lucky at a local store. (and I think one of the DS systems, DSi maybe, is region coded so you wouldn't be able to play it anyway :c) The third game has a story mode and a vocaloid song, too
Elite Beat Agents: Also pretty fun, with funny stories for each song. but it got boring fast, so you might want to just borrow this.
Rhythm Heaven: I hear so-so reviews on this, but I haven't played it. Hey, it's a rhythm game.
PuzzlePuyo pop fever: pretty fun and addicting
I think there's multiplayer mode, but you need everyone to have the game... (I think.)
Scribblenauts: Great fun, highly recommended. You can do nearly anything, if you can imagine it. That includes ride on a Pegasus with God, wearing sunglasses and wielding chainsaws. Yes, you heard me right.
ActionTrauma Center: I hear a lot of people like this... the story is ridiculous tho. You might not like it if you don't like blood, but it isn't that realistic xD And the first game is the hardest in the series, so you might want to skip it, haha. Helps you work on your focus
Mario Kart DS: because.
Super Mario 64 DS: (not sure of the title) but it's basically the same as the original for the N64, but with a few new secrets. A fun action/mario game for any gamer
Other/Casual Gamers**Animal Crossing: If you've never played it before it's kind of a must-play in it's own little category. Pretty addicting, and you'll spend hours on it.
Nintendogs: lul if you want something cute it's fun for the hell of it
Chibi-Robo: This is pretty addicting, but no actual story at all :'D
Not Recommended
Drawn-to-life: just no.
Spore Creatures: Very short, small, and boring. If you want to play spore, get the PC game