I think in the first level there should be more time until the lava starts rising, so new players have time to adjust.
When I reached the top the character just got stuck for a second or two and then I got a game-over-screen.

Interesting concept with great assets and animations in regards to make the players feel a sense of rush/panic when playing the game. Fast reaction and quick thinking will be needed in order to be able to beat the challenges win the game, as it involves the gravity of the character in the game of how high can he jump. The game is relatively balance, even though the volcano is a little bit too fast in the first level as it should be lowered in order to let players to get a sense of feel to the game.

Assuming there's no second level or it's a bug as I am unable to go to the next level and keep dying whenever I get to the top. (Game over page will appear suddenly)

Sound would be make a drastic improvement for the game polish so that player will be entertain, though sound can be hard to make.

things to put to make the game more interesting -

every step the player goes up will give him/her points.
This points will be able to use for the players to buy power-ups
put a shop that enables player to buy things such as rocket boost and many more

As the game as unlimited lives, this can serve to make players be addicted as they would grind to the level in order to buy as much power-up as they can in order to go to the next level.

This game has a chance to become a great game if polish/refine well
A job well done ^-^

Would be nice if you added some sound.
The concept is really good, but the game itself seems difficult. After getting to the top of the first part, I got a random game over. Also, if you're going to have a cutscene, you may want to add sound. The game feels a bit slow too, maybe you could make it so the character could run a little faster and make the lava a little slower on the first stage. All in all, Í can't wait for the perfected version of this, it has a lot of potential.