its simple and fun but i spotted some bugs and i have few suggestions also
1) You loose two lives if you fall off the platforms instead of one life. is this intentional??
2) The Screen size is really small
3) I like the feel of the game but the platforms are really too cluttered
Improvement:
Instead of using the ArrowUp key for jump, you can use the Spacebar.
That's all i have to say. and again it's a very nice game.