First person shooters on handhelds are meh.
QFT
I got a monkey ball game on the DS and the shooter was as good as a kid friendly game could be, with a variety of weapons and ammo. If i remember it was a cupcake which blocked your vision, watermelon seeds which i always used cause its rapid fire, and some type of melon that was a grenade. Then there was the default orange blaster.
CoD4DS should have wi-fi...if it did i would get it.