I had high hopes for Moon, for some reason. Wait, I know the reason: it was being positioned as a portable shooter with intriguing mystery/sci-fi elements. Sadly, it feels more like a tech demo than a game I'd want to invest any real time in. The fact that it feels fluid and maintains a high frame rate on the DS hardware is pretty incredible, but they obviously spent all their time on that, and then put the last five minutes into hacking together some story and dialogue. I sort of wish they hadn't even bothered--it's truly cringe-worthy.
It sort of plays like a Doom clone (the textures and 3d models are indeed circa 1994--that's how you get 60fps out of a DS) with some very slight enhancements, and an attempt at some Metroid-style game mechanic.
In the end, I don't know who this game is targeted at: people who like atmosphere and plot will be extremely disappointed, and surely most hardcore FPS fans (who might appreciate the high framerate) won't bother playing something at this resolution.
Also, the music is disappointing.