Nice game! I love the art style and good solid platforming challenges!
What I would focus on if you were to continue work on it is player feedback. Sound/particles on actions like jump/double jump/stomp an enemy. Initially I was confused when I fell on a side spike and it disappeared, then I realized falling on most obstacles would defeat them. Adding some sound for that action would help avoid confusion, for example.
Sidenote: I'm not very experienced in Unity but when I've used it in the past I've encountered the same jittery player movement and I believe the bug came down to where I put camera/player movement code, something was in the wrong spot either Update/FixedUpdate/LateUpdate. Something to look into (but take with a grain of salt as I don't really use Unity).
Overall, great entry I enjoyed it!