Once I figured out that you could only jump once and that it was always the first thing used, I changed my way of thinking and solved all the levels. I think it would be beneficial if you clearly stated this from the beginning, so that people aren’t confused by it. The level design was well done, and they made sense once I understood the rules.
The SFX worked well for the game. I agree with another commenter that background music would have been nice.
I liked that you started on the settings screen, making it easy to get into fullscreen. I also liked that you played the SFX when adjusting the sound slider, so I could get it to the right volume easily.