As much as the arena sections are visually more rudimentary and simple compared to the other parts of the game, I actually thought the art for the arena sections was cute and fun and I enjoyed it quite a bit. Especially the cube guys I think those goobs were lovely. The simpicity in the shapes and the palette are very apealling to me in a pleasing and almost relaxing way.
I did wish the arena sections had a bit more visual feedback when it came to the player's actions, specifically when it came to the dash. When I tried to use the dash I wasn't sure if the player character was faster than usual or not, and because of that I ended spamming it mindlessly, which is a shame because I think dashes in video games are great for game feel. I would suggest maybe adding a ghost trail like Celeste or just a trail in general next time you put a dash mechanic into a video game because I think it would help a lot when it comes to game feel.