I like how cohesive the design is. The sound effects support the aesthetic, and the fist that breaks the general visual style got a chuckle out of me! On a technical side, walking on a curved surface like the character's head was done so well I almost didn't realize I should point out how good it is.
In terms of improvements, there really wasn't much of a challenge. If I walk from left to right, constantly punching, and then right to left, I couldn't really lose. The only thoughts that I'd miss were the ones that clipped out of bounds when another thought spawned inside of them. There was also little to no reason to ever jump since the enemies very consistently spawned near the head.
Overall I had a pretty fun time with the two minutes I spent with the game to clear it twice!