Really nice concept.
Pros: As mentioned, the concept and theme. The (lighting? Is it lighting if its echo location?) effect used to represent the echo location looked really nice. The sound effect of the bat clicking, and then echoing throughout the cave is really cool.
Cons: The controls and collision boxes on the cave seem very unforgiving. It felt like I was dying without touching the obstacles at some points. This coupled with the controls being quite floaty made it very hard to play.
Overall, I think it needs quite a bit of tweaking of collision boxes, and maybe tighten up the controls. You got the aesthetic and mood bang on though. Good Job!