I really liked the cave sprites, overall the environment felt really well designed, the sources of air were far enough apart so that I did feel some sort of urgency to find the next pocket of air but there were also enough so that each time I did run out of air there was one close by, well thought out!
I found the overall premise of dave's situation intriguing, although I must say story wise it could've been fleshed out a whole lot more than it was. Since I don't think there was any plot points beyond, here's dave, he's stuck in a cave. (heh)
All in all a fun little game with really neat looking cave system!