great game
i think you should really consider making another one of these, iv got some pointers o help you out on the next one
1) ad some more calore, i just think grey is a little dull
2)make it longers
3) each world should have a theme eg the 1st 2 levels in world two had rising "lava" and if all the levels in that world had that, that would be a theme.
4) either get rid of the bosses or make them harder
5) change the mouse so that is some kind of charecter, this is kinda a stupid idea since it would probably make it harder to get though narrow tunnels and stuff but if you make it work i recon it would be a great idea.
6) make the lines dead straight(although the rough lines give it a rustic style, it also makes it hard to determine wether or not youll make it though.)
i hope you put my ideas into practice.
btw if you reply to this reveiw could you let me know how long it takes you to make a game like this