Eh...
There's a lot about this I didn't like, and only some parts I did.
I thought the game was conceptually well thought out, and I enjoyed the soothing music as I played, nothing too distracting or loud.
However, despite being wonderfully conceptually driven, I thought it was poorly executed. Very slow, sluggish controls for the character. The art was rather grungy and really nothing special at all, but with a game like this I don't think art is as important as level design and coding. So with that, I thought the level designs were rather simplisitc most of the way through. I felt that because of the sluggish movement of the character, differing from the movement of characters in most other games, judging where your character was when you were invisible made it more tricky than need be.
I thought the game was okay at best, but I'm giving a few extra points for concept.