There are a lot more better shooters out there, and having a shooter on the DS sounds cool and new but its not all that good. This game lacks a lot of content, the bosses aren't so good I find and like in a few other reviews, this game is very repetitive.
The graphics are great for the DS, but that's the best part I would say. The gameplay is annoying with the stylus because you push it harder and harder into the screen as you play, especially in the boss fights and so your hands start to hurt. It isn't fully adapted for the DS, and if your looking for a shooter, go with PC, 360 or PSP.
The hand held shooters don't seem worth it to me because you can get a lot better at a cheaper price, if the DS is the only console you have and you don't have a computer, then you can't be reading this, but if you ARE reading this then I say stick with your comp. for shooters.