This is a pretty straightforward platformer, and what happens when you make a game like that is the small things really stand out. So the slowness of the movement, the sometimes glitchy behavior of collisions, the floaty jumping are a lot more noticeable. I'd focus on fine tuning those aspects of the game, and then layering in more elements like more hazards, music, different mechanics, etc.

I think this game would be a bit better if the player moved a bit quicker since the player was so slow it made it hard to jump over the lava. Also when you die it sends you right back to the beginning making it quite tedious. I think if you fix them things the game would be a lot better :)