A short but great game. I really like how we really have to think quickly about what to do. Though, knowing that each level always have the same layout kinda makes it a little bit trivial to do. I guess that's kinda how these types of games work.
Just a suggestion. Maybe add an endless mode or something similar with procedurally generated levels? Or at least randomize the positions of the enemies, key, door, and exit. It could coexist with the normal levels.
I do agree on the other comments. The game is a little bit slow to play and could be a tad faster.