Pretty fun! I liked the various level designs and the smooth functional controls. A bit too much relying on the jumping to the (1 up and 2 left/right) as a puzzle mechanic, which could get difficult at times with the player hitbox. Nevertheless, a solid entry.
The player being the same size as the blocks make some of the jumps a bit too hard. Apart from that I really enjoyed the music and the lava physics were impressive.
I'll have to echo the complaints about basing one's head against the block above, but other than that it's a good game. Filling the cavern was a good idea, it gives players less time to loiter around the level and forces them to think quickly.
Using CA is a nice touch - you definitely have a big plus for having interesting physics in your game (although I wouldn't recommend thinking of CAs as physics models per se). There seems to be a little /graphics-connected/ inconsistency when lava is falling down to one spot - it doesn't fill the tile, like it would do when spreading horizontally, just changes it's opacity. I didn't look into it though - perhaps it's a limitation of the model. Anyway, I've seen similar mechanics in a few games, but I think it's fairly innovative for a LD Compo. The game is pretty unforgiving and fast-paced, but it does restart at the beginning of current level and there are unlimited continues, so the difficulty seems reasonably balanced in my opinion. It's hard, but retro-style hard, which is more than acceptable. Humorous comments of the main character are really great, and music is also pretty neat, btw. Oh yes, this is a very, very good entry.
Could have been better if there weren't so many jumps with a block directly over the players head.
Needs better level design but good work overall.