I've played many DS games this year, all of which I have resold or intend to resell. The games I purchase are based on reviews and my own judgment. These are the games I have owned this year (in no particular order):
Nintendogs: Daschund and Friends
Yoshi's Island
New Super Mario Bros.
Sonic Rush Adventure
Trauma Center: Under the Knife
Mario Party DS
DK Jungle Climber
Brain Age 2
Flash Focus
Worms: Open Warfare 2
Kirby Canvas Curse
Clubhouse Games
Pokemon Pearl
Advance Wars DS
I usually sell them after I complete them or whenever I get bored of them. So here are my reviews...
Games to buy:
Sonic Rush Adventure - This is the best DS game there is. I have owned it for about 2 months and still play it daily. The lastibility and replay value on this game is amazing. Replay includes finding all the hidden islands, completing all 100 missions, upgrading all ships, and obtaining S scores on every level.
Worms: Open Warfare 2 - I enjoyed this game because of the resemblance to the PC versions but I finished it in a couple weeks and there weren't enough people to compete against online to justify keeping it.
New Super Mario Bros. - This game is cool but after beating it and collecting all the coins, there is nothing left to do except get rid of it. The replay value is limited.
Other games to consider: Yoshi's Island, Pokemon Pearl, Advance Wars DS
Games to stay from:
DK Jungle Climber - I played this once and got rid of it. The controls were too annoying and not fun at all.
Flash Focus - This was just too boring.