I didn't like the acceleration and jump curve of the player.
The jump felt like I'm continuously giving for upwards to the character which isn't realistic nor good feeling.
I didn't feel the character really being influenced by gravity either. With some squash and stretch and speedier fall, that would've been better.
Speeding up didn't feel snappy and the player is maybe a bit too slow as well.
These problems could be relatively easy to fix either by just tweaking parameters and/or looking at how other people coded responsive and juicy platformer controls. Good luck with learning this :)