Good work! The movement feels very smooth as far as I'm concerned. Coyote time, jump buffering and all that good (must have) platformer stuff.
I don't have much experience in terms of puzzle design, but one thing regarding platforming I'd like to point out, is that if you jump via a jump buffer (i.e. press jump before technically having landed yet), it gives you a lower max jump height compared to what it is normally (not sure if the base jump height is affected by this, or just the max jump height).
This is not a big deal, but a few of my jumps were unfortunately thrown off by this very thing, because I tend to chain jumps whenever I can in platformers. It made the jumping feel kinda inconsistent.
Also after finishing a level, I personally think I would prefer being spawned right outside the level I just finished, instead of at the entrance of the hub. It was a bit tedious (I'm being nitpicky, I know :P) to walk past all the finished levels to reach the next.
All in all, very nice demo, I look forward to seeing more :)