I finished the game. The difficulty seemed okay, or maybe a little easy; I got through the levels in one try, or two at most. I was actually glad that the platforming wasn't too tricky, since that might have been annoying when combined with physics. More difficult puzzles would be nice, though.
The speed seemed a bit slow - perhaps you could increase timescale, if that wouldn't cause problems.
Overall, everything worked well, but it could have been more interesting. The part I liked most was when the jumps were introduced, because that made the gameplay more complex. I think the game might be better if it had elements that can combine to make the levels more devious - gravity-reversing switches, fans, tethers, balloons, something like that. Or maybe more abilities that you can pick up other than 'jump' - like repel, swap places, etc.