Cool effects on the player and platforms! Regarding the movement issue, I think a lot of it stems from how high the 'gravity' is, which makes it so that you have to give the player a lot of jump force to counteract the force pulling down (which is what makes the jump feel 'jumpy'). As a 2D Platformer, I think my game is pretty similar to yours so feel free to check it out if you want to try out 2d movement that feels different (mine also had comments about certain movement issues but they don't seem to be the ones yours has so it might be beneficial to try it out anyways!)