I'm going organize my experience according to the rating categories, hopefully it provides some useful feedback!
Fun 2/5: The low rating here is mainly due to the immense difficulty that hits pretty early on. The first level wasn't so bad, but the second was pretty rough, not helped by the jump, which I felt was just a bit too weak. I managed to make it to the fourth level before giving up. I think upping the jump velocity just a bit would be a huge help. Also, the round collider on the character does make sense, but it's a bit too easy to narrowly land on the platform only to slide right off. This is another thing that a little more jump might help with. I can also see how a gamepad would help a ton, I tried it and the jump key (A) was not working. I don't know for certain if that's a bug or is on my end, so I'll leave it at that.
Graphics 4/5: Nothing crazy, but does fantastic with a very minimalistic style. Does the job and does it well.
Music/Sound Design 4/5: Again, nothing special, but it absolutely does what it should and helps the experience. The song is just ambient enough to not become too annoying, sort of like a binaural beat playlist, it helps you focus, which is awesome!
Concept 3/5: Simple but enjoyable platformer. It really does not have anything to do with the theme as far as I can tell, but that is not a category for rating, so that won't play into my review here. I think a few tweaks to the gameplay (and the difficulty especially) would really improve this one.
Congrats on finishing your game! I'm pretty sure we all know that's often the hardest part.