Ah, lovely platformer! I faved this art kit too hoping I could do something with it, I'm glad to see that someone else chose it too!
I agree jumping with the up key is a bit strange, but the overall game feel is really nice and there is some nice polish too in menus ands sfx.
I would have change the spikes color to something more visible like orange or red (or just a solid color maybe?) cause they tend to blend into the background.
Also level design is great, with a progressive introduction to mechanics and new enemies.
Great work!