You've got quite some feedback already, and I can echo the general sentiment: It looks pretty great, with nice gameplay!
So here's some criticism, then, in no particular order:

Some animations , mostly the hanging-and-climbing-on-the-ceiling, seem... off. And I'm not talking the nonexistant transition-animation from Superku to Totally-Not-The-Morph-Ball-From-Metroid-Honestly-Guys. I'm not an animator, and thus my feedback can't really go more detailed than this. In my experience, you can either get lucky and get away with just adjusted animation speeds (sometimes, if the animation speed is a bit off compared to the corresponding character movement, things look off and wrong on a more subconcious level), or you'll have to face redoing the animations. I know animating is difficult and I am sorry.

The turning speed is too slow. Can you increase that? Compare with how fast Mario turns around. I think it would help make the game feel more responsive.

Superku seems a little too symmetric. It's not very clear from it's silhouette (which is what we see at a glance) which direction he/she/it is facing. The way I see it, you have two options: Making the cape much thicker, or making it's face bigger. As it stands, those two things are a bit hard to make out.

To help with those things, consider adding some particles that highlight certain positions. Consider a few smoke particles coming up whenever Superku lands after a jump, or a particle effect when you grab a ledge - especially the ledge grabbing seems hard to notice. Perhaps there is a sound, but there should also be a visual cue thats much less subtle than the animation. Also, particle effects when Superku runs up a wall would help with judging how much longer he/she/it can stick to that wall.

The sine wave ropes ... don't you think their amplitude is a big large?

Does the wind affect gameplay? It's hard to tell from the video. I mean, it's not a stretch to assume it does, so make sure to convey it early in a safe, controlled environment whether it does or does not. And once you decided on one thing, stick to it - either all wind-effect-levels have the gameplay effect, or none do.

I am still unsure what to think of the square-landscape-effect. Hmm.

Why can the doors marked "5" be destroyed with that laser-thing? This doesn't seem intuitive. Also, the power-blocks -- is it really necessary to move those two spaces? Yes, this is nitpicking.

Also, some levels seem insanely convoluted and big. It's fun to watch you play through it, since you know where to go, it seems fluid and like theres good progress being made at all times. But I bet if I were to play them, I'd get lost, miss some elements and generally spend some time idly wandering, destroying the flow, one point of criticism I have with Dustforce as well. Consider the room at 4:43 in the video. First, there's no signal or sign to go there first. Second, once you there, I'd probably press the button and think that's it, but no! I have to go upwards to a room I couldn't even see before and do a button puzzle there.
I'm not saying that you'll have to redesign all those levels, but you should probably add signs or other elements that guide the player more or less subtly around the levels.


Okay, that's all I can think of for now. I hope I didn't come across as too mean!
Remember, I do like what I'm seeing, and I think by fixing the above issues you could improve this game quite a bit!