This is one well made game! Very challenging gameplay and the progression of difficulty was just about right.
The art is great and the mechanics smooth. I really loved the way you designed the levels for each of those special abilities.
There are three things I think you could improve:
1) Keyboard button layout for people who would like to use their right hand. It was easier for me to use my right hand but at the same time hard to position it at an angle so that I could use the Z & X keys. Maybe provide the option to use the arrow keys as well?
2) Due to the fact that the player is always moving to the right, many times the coins that I collect would fly across the screen and either cover the player or just distract me; so I often lost sight of the player, which got a little frustrating in the more intense levels
3) For windows, maybe you could add an option to increase the window size, maybe just use surfaces to stretch what is displayed. Because it was often a little hard to notice the player because of it's color in relation to the background and environment
It was a fantastic game that I really enjoyed! Thanks for putting time and effort into this, it really is something great!