Looks good and I had fun playing it. Like most comments, I had problems getting on some platforms.
I found if I had some forward momentum when I hit the top, I could get on the platform every time but if I was standing stationary before jumping, I couldn't.
It seems that he is jumping so the base of his collision bounds are at the same height as the top of the platforms collision bounds. If you set the jump height just a couple pixels higher, it may clear up the problem.
Other than the jump issues, I thought it was a very good game.