Super late to the party, saw the feature on RPS and grabbed the demo. I created a new thread, didn't see this one -- sorry must have been tired, I'll delete the other one.
Lot to love here, only 30 mins in, but just a wee bit of feedback / intial thots, hopefully useful.
The smoothing on the camera feels off to me. It's a bit too slow to recover, with a bit too much overshoot, and at the very end of the recover the overshift causes the hero to jitter for a frame or two before it comes into focus again. It makes me a bit motion sick. Are you using floating point values to position the camera? Perhaps fix it to integers and work the math to ensure you're never in-between pixels.
Also on the camera, I feel it would be useful to explore a Mario style camera where you only pan up / down when changing surfaces, rather than directly tracking the hero's movement 1:1 w ever jump. The current system makes the camera too "active" causing me to focus on the entire world rather than just my jump and target destination.
I think there might be a bit too much slide when changing directions and maybe a bit more slide needed on the end run. Nothing major, just a few frames less and more.
Anyways really like it so far.
Sorry, don't remember the name. When I "pick it up" by pressing X the entire game slows down to about 1/4 speed. This goes away if I load into a new room, but there doesn't seem to be any other way to make it go away. At first I thot it was a neat effect of consuming the box, like I was burdened by it, but it seems to be a bug as it doesn't go away when I release the cube.
All the best!