Great use of aesthetics and theme. The controls felt pretty smooth except for the jitter when colliding with walls. I have had similar problems with collision jitter in games that I've made.
I'd have to see your code to really give advice on how to fix this particular case, but I'm guessing that the character is translating into a collider and then getting immediately pushed back out. (That was always the case when I had this bug.)
The way I solved this was to have multiple 'bumper' colliders on the player character - one on the left, one on the right, one up, and one down. When one of these bumpers is currently touching a barrier, the player character won't even attempt to move in that direction, regardless of player input. That eliminates the jitter because the character is not trying to force themselves into a collider!