The idea is good but several things took away from my enjoyment of the game. The long buildup to the volcanic explosion, where I just walk in a straight line and then fall down a cave was extremely boring. Then, after my "rebirth" from the lava, the jumping physics were rather annoying. For instance, sometimes the jump button wouldn't work, so instead of going up and over, he just ran off the edge. Also, the fact that I stop moving forwards if I hit the edge of a platform meant that I was dying much more than necessary. Polish the physics and intro, and you've got 4 stars from me. As-is, only 2 stars.

Because it isn't fun in the slightest...

This game is almost impossible to play. The jumps expect a lot from you, especially since you're so slow and your jump has such little strength. The first minute was spent simply holding the left arrow and waiting for something to happen. Once you get your agility heightened and such, the jumps are still almost impossible to make. However, the music does set up the atmosphere very well.

you can't even jump high enough at one point to get out of the volcano...

The game itself is alright for a practice game. I like the way you used textures, masking I'm guessing?

A few recommendations in-case you're wanting to go deeper into flash:
Have tut-tips! example would be at the beginning here tell the player to use arrow keys.
Start using pre-loaders, especially when the file size is this big.
^ don't make the file size this big :) use compression to scale down the music size.
Get a decent sound library for sound effects, it drastically enhances the game.
Reduce time it takes to get to gameplay. (Average flash game play session is 4:28)
Keep the gameplay responsive, such as unrestrictive movement like jump+move viable.
Implement scoring systems and high-score tables to allow competitive gameplay.
Always have a non-biased tester before release.

Anyways, good job programming the engine, it's quite nice. Keep working at it and you'll have a great game in no time ^_^

Best of luck to you,
~Jo