I liked the concept op the game but there are still some things you could improve:
- give it some music. a game with a soundtrack is instantly twice as good. but then, don't forget a mute button :)
- I was able to cheat in the Volcano.. if you jump against the left wall, you can keep jumping until the top of the level. you could avoid that by forcing the player through a horizontal tunnel.
- put some respawn points in the game. Currently i am stuck in the cave but im getting frustrated because i have to do that first walljump over and over again, after i died..
Overall it is a good game, so keep up the good work :)