HM. I think I found a bug: In chapter 4, I was able to go all the way to the left, and dropped off the screen (there's a bar at the bottom I was able to see as I press left or right, but couldn't see my character, and couldn't seem to do anything else).
Also couldn't figure out what to do at that part before that -- couldn't QUITE make it onto the ledge at the far right either. I'll give it another go.
That aside, very nice game. :)