The slime has a good weighty feel to it and its fun to swing it around and drag it behind you. I think some of the narrow ice spaces were a little too narrow, or that the penalty for dying was a bit too much. Maybe if the buttons stayed pressed even through death, or a checkpoint? The other suggestion I'd have is to have the camera go ahead of the player when possible, maybe using the mouse position to influence where the camera is.
Overall this felt really good! The controls felt really responsive and I can tell you spent a lot of time tuning that.