I don't understand the bad reviews; GERA is the DS's first FPS, and pins the tail on the donkey!
The gameplay is solid. A lot of what you do is through the touch screen such as reloading, switching guns, eyepowers. Health and armor is also down there, eliminating HUD on the top screen so none of the tiny screen is clogged. The controls are akward, though, and since my hands are kinda small for the thumbstrap, and it's awfully impercise, I'm forced to use the stylus with my pinky on the R button. Also, sometimes your aim jumps around (Even though the framerate is steady). Maybe it's just crap on my touch screen.
The 3D graphics are very good for the DS, although it's hard to see distant enemies. Maybe it's cuz they spawn randomly. Whatever.
The sound is OK. Nut as bad as some people are saying though. Some of the tunes are catchy but all of the SFX are very pixelated.
Underappreciated. Yup. Better than advertised. If you're craving for a DS FPS, look no further (right now). If I could have three games ported to DS, they'd be Goldeneye 64, Perfect Dark, and maybe Quake 2. Oh yeah, the AI is dumb and stationary at times, and know-it-alls other times.