Animations and artwork are great! Atmosphere is captivating.
Agree with some of the other posters that the controls feel awkward. A large part of that was the first level, where I was confused by the fact that I couldn't use sonar. I guess that, since it's not needed in that level, it's not available. Still, that made me wonder if there was something wrong with the game or with my keyboard.
In 2nd and 3rd levels, the different ways of seeing were interesting, and added a lot of tension to the exploration experience.
Cool concept :)