I admit when I started playing this I said, "OK, so you walk around and bump into walls, and those are the walls. Kind of...basic?"
And then: the other tiles! Suddenly it became much less trivial, and genuinely interesting. By the last level, I'd have almost everything mapped out and be walking back and forth trying to figure out which thing I'd marked as floor space was actually a tunnel.
In terms of gameplay, a few things that struck me (which I mention only because you asked for criticism, and I'll emphasize that the game was still fun, none of these are dealbreakers!):
- Obviously the graphics are a little simple. Perfect for a prototype or an experiment; might want sprucing up for a full project.
- I'd love if the "level complete" box didn't cover up the level, or gave you a chance to clear it before moving on; often I wanted to look things over. (You can probably draw inspiration from a lot of other games that have a "level complete/next level" pattern.)
- There were a few cases where things were technically ambiguous. For instance, if a corner space has walls on both of its sides and you can walk onto it from both walls, it could be a wall, or it could technically be a ladder. Similarly, if you can't walk onto it, it could be floor or it could be ice, on levels where both are available. (I didn't investigate whether the game accepts a particular solution or any valid solution.) It's mostly harmless, but I think puzzle games work best when there's no ambiguity.
Good luck with future projects!