I've been playing for about an hour or so and so far this game is fantastic. The pace, atmosphere, sound, and controls are wonderful. So here are a few quick thoughts...
Let's start with the controls. Have you played Metroid Prime: Hunters? If you have, AND you liked it. Then you will will be running and gunning in no time. The control scheme is simple and effective and fast. Your D-pad is for moving (forward, backwards, strafing left and right). You look around with the touch screen, and this feels so natural after about 5 minutes if you've never played an FPS on the DS before. I highly recommend you purchase one of them wrap-around stylus thingys that they have. You can basically turn your thumb into a stylus with one of these and it will make playing the game so comfortable.
Ah my trusty flashlight. I've missed you since Doom 3.
The puzzles are what you would expect from a survival horror game, but the action is fast and frantic. I often find myself running like hell for the door just to get away from the occasional hoard of monsters. So far I've only found three weapons but there looks to be seven or so in all (not including our trusty light).
The sound is probably the best part. Dementium has some wonderfully sad melodies to listen to while you beat, chop, and shoot the vile creatures that have over taken this facility. I can't wait to get back to this game... so I'm done. Need to play moar!