This is brilliant, the use of sound quality and pitch to simulate echolocation works perfectly. I have not tried the game with a gamepad, but it plays very well with a keyboard. There are a few issues I'd like to address that I think could push this game to the next level though:
This is a game designed for blind people, but people without visual impairments have a distinct advantage when playing this game. Since "accessibility" is the theme, I think it would be cool if you leveled the playing field by taking away the visuals completely. I can play this game entirely by sight; the sonar is a key aspect, but for the sighted it is unnecessary since we can see every wall, obstacle, etc. I think I would have more fun if the game forced me to play the way a blind person would play.
My other suggestion is to include a short tutorial level where you explain what each sound effect means. Without being told so, a blind person isn't going to know that the "dangerous obstacle" echo sound means danger, they will only know that it sounds different from everything else.
Great work though, you've got an excellent game concept here and I wouldn't be surprised to see "clones" of this in the future.