I don't think the game is that hard, on the contrary it's fairly easy and it takes all of a few minutes to beat. Still the difficulty curve is too steep (a few easier levels to start things off, then ramp up in difficulty would be a better approach). Additionally a lot difficulty comes out of badly sized collision boxes which are too large. The controls are really good though. Tight and precise as they should be. The jump could use variable jump height depending how long you press.
The sounds are not good. They don't fit together even if their loudness were the same. The jumping sound is badly implemented, it plays when a character falls from a platform (which it shouldn't) but doesn't play on the second jump when it should. Additionally it gets cut off abruptly when the character is no longer in the air. There's a sound indicating starting movement (or continuing movement when landing) which doesn't seem useful, but there's no feedback sound on landing on the ground.
Music choice is nice but it's placed nonsensically. The loops are cut too short and are drowned out by the other sounds.
The same aesthetic incoherence goes for graphics, everything follows a different style and doesn't create a unified whole. Still despite that, the game is visually clear, which is good! It is never confusing what is background, what is foreground, what is an enemy, etc.
Aside from the zombie, you have a few different spiky enemies, a few different looking spikes and fire which all serve the same exact function of a static obstacle. There's no need for this much variety, especially since their visual styles don't work together.
There are other minor bugs with sprites and animations. The player randomly disappears for a frame. The zombie is floating and not touching the ground. Fire is jumping around which could be fixed by adjusting the pivot of sprites better, or slicing each sprite the same way.
As for the stuck on walls comment above: here's where I was able to get deliberately stuck.
wall stuck.jpg