Really like the puzzle mechanics. The click of the keys is pretty satisfying.
I got stuck on level 2-4 so I can't say much about the rest of the levels.
Some of the behavior seemed like it was inconsistent with holding keys. For example, on 2-4 at the start, if you hold down and and then right at the start, you'll go all the way to the right without dropping down. If you hold up and then right, you go up the very first upward passage.