Ok, so, I've played the C3 demo and I'm gonna try to word this as nice as possible.
As good as your visuals are, they're really the only thing driving this hack.
Your levels all play it too safe, they feel too repetitive and samey.
The only thing telling them apart is "this one has X sprite" or "this one has X graphics set".
If you remove the aesthetic theming and the "gimmick" (which usually isn't really explored much) from most of them, there's nothing to distinguish them in terms of level design or difficulty.
They're all over as soon as they begin, just hold right and jump when needed (outside of the Blue Switch).
I'm not saying this to get on your bad side, I'm saying this to help you improve your level design.
NSMW1 had the exact same issue and that's why I gave up on it at the cave world.
Sorry if I'm being too rough.
Hack・
Ports・
ASM・
"Uploader"