Surprisingly, this is a fun game for the DS with great online play.
The graphics are surprisingly good (for the ds) and the gameplay is, in my opinion, as good as the gameplay of the PS2 version. (Please take note that the 360/PS3 version, PS2 version, and ds version are like completely different games, with different stories and levels.) The controls work as good as possible for the ds, and are very easy once you get the hang of it. You move with the D-pad, aim your weapon with the touch screen, and shoot with the L shoulder button. There is a large variety of weapons such as the flamethrower. There are also some levels where you control a plane or a tank. The voicing in this game is great for a handheld system. There are about 28 achievements you can be awarded in this game for doing stuff like getting a certain number of kills. There are also 30 challenge levels where you must complete tasks in a certain amount of time.
The online play is the best part about this game in my opinion. There are quite a few different maps you can play over the wifi connection. Up to 4 players can play together on a map at once, as teams, or as individuals. 4 players may not seem like much, but is still quite fun even with only 4 players. There are also other game modes for online play such as capture the flag, where you must get the flag that is randomly generated on the map and return it to your base. You can keep up with your stats of wifi play (and regular play) and view kills, deaths, wins, losses, and more.
Overall, this is a great game for the ds. I find myself playing the ds version more than the home console versions. If you are a fan of Call of Duty or FPS in general, I would suggest getting this game.