I've been following you on Twitter for a while now so I'm very happy that I finally get to try out your game. It was really good. The level of polish on the graphics/art/aesthetic really shows. I liked pretty much all of it but I'll go into the things that really stuck out to me below.
I really liked the two movement power-ups (i.e the spin dash and the paper airplane). The airplane animation is very good, and using it to traverse the large gaps of the island was fun (i.e. over to the lonely island with the lime).
I really liked interacting with the bridge that you hit your head off (after bouncing on the trampoline) and knock over onto the ground. When I did it the first time the bridge fell onto the trampoline blocking it so I had to bump it off the map. I always like playing with dynamic pieces of the environment.
I really like the post-processing filters as they give a new flair to the visuals that I can cycle through. I especially liked the cinematic one.
I only have two minor gripes. I think the Player/Equipment menu screen could be better laid out. I kept expecting the 'Outfit' section to be it's own part of the menu rather then a sub-part of the Equipment section (i.e. I kept pressing right when my cursor was hovering over the 'Equipment' badge expecting to the Outfit area of the menu rather then the Power Ups area).
I also felt like the jumps could be slightly more lenient/the standard jump made slightly longer. I kept falling into holes which I don't think were meant to be a challenge (e.g. the little hole before the dog that sells you the mallet).
I also found some glitches which you may or may not be aware of:
1) If you pause the game while you're in the air your downwards velocity(?) is still being updated in the background so if the game is paused for a while you slam vertically into the ground. (e.g. pause the game halfway through a jump -> sit on the menu for about 10 seconds -> unpause the game = slam fast into the ground).
2) The pause menu portrait of scrap girl only appears if you equip the scrap girl outfit in the first zone of the game (the heavily forested area) and disappears if you move into any other zone (e.g. Pick up the Scrap Girl Outfit Card -> Walk into the area with the broken bridge -> equip the Scrap Girl Outfit = Pause menu portrait is still blank.)
Hope that all made sense.