Bugs/Errors: The wall jump lets you both skip portions of the level and get over the barrier to the left at the start.
Strengths: The artstyle and atmosphere are really great, plus the character is fun to control (I brought up the bug with the wall jump but I had fun doing that) and you can easily tell what every movement is supposed to be.
Weaknesses: It could be a bit clearer that you can pass through one of the platforms by pressing down.
Changes or improvements: I imagine you will add this in later, but giving you the ability to pick up the collectibles would be good.