Hmmmm...
The only thing that's bringing the score down for me is the difficulty. The concept was pretty cool and I guess the harder it is it more represents being blind, but some parts were incredibly frustrating. I think if the sonar was able to display the environments more clearly (I strained the hell out of my eyes; maybe that was the point?) or some of the jumps didn't require absolute precision you could make it a bit easier without losing the artistic feel.
The only other comment I have is that I felt almost disappointed by the ending. I guess I was expecting a clearer picture of what all those objects were (and that weird O at the bottom of level 17 or so...) and what this blind guy looked like. I mean I spent a good couple hours (not in one sitting) getting through 21 super hard levels trying to figure it out (used the walkthrough A LOT) and my only sense of relief is the ending, which just seemed...lacking. Great idea, though. I just wish it wasn't so damn hard.