Pretty good. Some of the puzzles were a bit of a challenge and took a bit of thinking. A lot of them were fairly straightforward, and I feel like a couple of levels either had boxes and other special blocks that were purely red herrings, or the levels had unintended shortcuts.
One small bug to report: pressing up/down while the slug is moving causes the page to scroll. I'm just guessing, but I suspect a "preventDefault" is misplaced and only being called when a move is actually triggered, so gets missed during the move animation.