It's enjoyable so far, but one comment: For a 3D platformer, I would recommend making the player cast a shadow on the ground so people can tell where they are when they're jumping.
Since the player's character is 2D, probably the best way to do it would be to attach a 3D sphere somewhere high above the player (outside the visible space when playing) and add a directional light to the scene pointing straight down with DirectionalShadow set to Orthogonal. As long as the walls/ceiling have their cull set so they're not visible if you look at the scene from above (which looks like it's the case) the ceiling shouldn't cast shadows and you should be able to see the player's shadow -- I'm doing that in the game I'm working on now and it seems to work well. If the ceiling is casting shadows so you can't see the player shadow, and the ceiling and floor are on different meshes, you could go to the ceiling's MeshInstance under GeometryInstance - Geometry and turn CastShadow off.