Pretty good!
I like the game, it's simple and easy to get into, the jumps get challenging in some areas. Overall it's very nice. There seems to be a few glitches in the game still, for instance on the level where the disappearing striped platforms first appear, if you jump off the first spring and hold left the entire time you can jump out of the level.
One thing that bugs me about this game, You should make it so I can press "X" to go to the next level instead of making me click a button with my mouse. The game doesn't use the mouse, don't make my hands leave the keyboard every level :)