Really cool game, I really enjoyed it! The gravity switch mechanic was cool, well-implemented and used well in the level design. As many have mentioned before I think you could use one button for the gravity switching though, as I sometimes clicked wrong button because I forgot which one worked when. Also, it would be nice if you didn't change so that jump was on "s" when standing in the ceiling, and instead always on "w", because it was a little disorienting for me.
But very cool game, I enjoyed it. It is pretty challenging, but I think that is good and fun. Also, good art and music.