Awesome game! I'm a little surprised this game has so few ratings. More people should definitely give this one a try. The swapping mechanic is handled very well, and the game looks and sounds great. Probably one of my favorites that I've tried out this jam.
I think if there's one thing I would change, it would be to add enemies coming in from multiple directions. In the first stage it's very easy to just sit in the middle, wait for an enemy to get close to the bottom of their tile, and then swap the enemy's tile into the bottom row, forcing them to immediately walk out. It makes the difficulty pretty trivial, but I think if stuff were coming in from all directions then that would lead to much more interesting decision making.
Good work on the game though!