I purchased a black Nintendo DS Lite in late 2006. At first it wasn't a handheld console that I wanted to purchase (the gimmick of the touch screen is not really necessary in the kind of games I usually play on handhelds), and was very tempted to buy a PSP instead, until a fellow student from my university showed me Osu! Tatakae! Ouendan... 10 days after that, I purchased the NDS and imported that game...
Osu! Tatakae! Ouendan (2005) A rhythm video game that made me decide to purchase the console. Is about a manly cheer squad cheering for various troubled people, that sounds really weird (and, in fact, it is) . The crazy story mode, the overall setting and the 15 songs featured are really good. Since it uses fully the touch screen, is really hard to do a similar game in another platform (but Hatsune Miku Project DIVA was similar enough...)
Moero! Nekketsu Rhythm Damashii Osu! Tatakae! Ouendan 2 (2007) The sequel to the former. Includes a playable "rival" cheer squad, and a bit of improvement in the gameplay (now you can skip the cut scenes until the very beginning of the song, for example), but the 19 songs included are in overall weaker compared to the prequel.
Elite Beat Agents (2006) The spiritual sequel to Osu! Tatakae! Ouendan for the western markets. The ones cheering in this game are agents from a secret government agency, and the 19 musical themes are all of western origin, but the overall gameplay is the same. Not as good as the Japanese counterparts...
THE iDOLM@STER Dearly Stars (2009) Really not as good as I expected. The original iM@S games are hard to tag (musical raising simulation game?) and the DS version manages to butcher almost all the aspects: the stats of your idol means nothing, the auditions are just a mini-game between chapters... The story and the characters are not bad, so is not a complete waste, but is not really iM@S game.
Phoenix Wright: Ace Attorney (2005) Is the port of a Capcom's visual novel for the GBA, released in 2001 only in Japan. You play as the defense attorney Phoenix Wright and you objective is to win in a wacky courtroom. I don't like the localization that much (I hate when people try to "westernize" names and places), but despite that is really an enjoyable game.
Phoenix Wright: Ace Attorney Justice for All (2006) The second installment of the series, introducing more memorable characters like Franziska von Karma.
Phoenix Wright: Ace Attorney Trials and Tribulations (2007) The third one and the last that was originally released in the GBA. Possibly the most well rounded one.
Apollo Justice: Ace Attorney (2007) The first one that is not a remake. Maybe because almost all the old characters were dejected in order to begin a new era with brand new characters, but I didn't enjoyed the game as much as the first ones. Still is a nice game per se.
Another Code: Two Memories (2005) Known in North America as Trace Memory, is a little adventure game that creatively uses the unique features of the NDS to solve the different puzzles. A bit too short.
Hotel Dusk: Room 215 (2007) Another adventure game by the makers of the previous one. Longer than Another Code, is more oriented towards an older audience (after all Kyle Hyde, the main character, is a thirty-something years old ex-detective, while the main character of Another Code, Ashley, was thirteen.)
Nintendogs: Chihuahua & Friends (2005) The extremely popular pet simulator. It was bundled with the NDS when I purchased it. I only played with a Yorkshire Terrier puppy (the same breed as my real life one) for a week or so, and never again touched the game. Now the poor puppy must hate me...
Big Brain Academy (2005) The other game bundled with the console was this one. A Brain Training/Age wannabe more focused in mini-games. I kinda dislike this kind of "casual games".
Trauma Center: Under the Knife (2005) A "medical simulation game", is really a series of mini-games driven by a visual novel styled plot. Is enjoyable to play (except the X-missions) and I must admit that one of the motives that made me buy the game was the visuals of the nurse Angie Thompson (the blond in the cover).
Final Fantasy Fables: Chocobo Tales (2006) A series of Final Fantasy themed minigames. Way too childish, I bought it only because was only 9 euro.
Final Fantasy III (2006) An enhanced remake of the original Famicom/NES game. I highly prefer the stylized character designs by Yoshida Akihiko over the ones that appears in the CG movies. The similar Final Fantasy IV is in my wishlist.
Chrono Trigger (2008) A port of the original 1995 SNES version with added contents like the movies that comes from the 1999 PSX version. As I said in the entry when I purchased it, this is probably the best RPG from the 16 bit era.
The World Ends with You (2007) I think this is the best Square game released in the last 10 years or so (no including the remakes and ports). Visually similar to Kingdom Hearts, is truly a completely original RPG, taking place in the modern Shibuya instead of a fantasy world.
I think this game is the only RPG that takes full use of the touch screen (normally the lower screen is used to display maps and buttons) : you must touch, scratch, drag and blow to the mic to use some of the in-game attacks, and both screens are used during the battles.
Etrian Odyssey (2007) An RPG with old-school flavor. Very difficult, even with a max level party and the best equipment you can get easily owned in a mere random encounter. One of the features of the game is that it doesn't have an auto-map, and you must draw one in the lower screen. Also remarkable are the cute character designs by Himukai Yuuji.