The good:
Everything from music to graphics to level design and GB feel! Mayybe some things such as the selection screen feel a bit too archaic in comparison to the GB (seems you're changing scenes instead of redrawing tiles for the changes) but that's just nitpicking, because the rest is impolute! Very charming and absolutely impressive for a jam entry.
The mixed:
Was it really required to have the items as enemy drops and making you lose them at a hit? I found the backtracking a bit tedious ngl, I prefered reseting on some ocassions instead.
The bad:
The spikes are unfair! when you approach them from the sides they shouldn't kill you, lost countless times to those. Also the trash bag in 1-5 doesn't read as an instant death thing, I find it very annoying, I'd prefer it being friendly but dropping oil to mess up your movement, or anything else!