Just finished playing and this was pretty enjoyable. Not too easy, not too hard.
I agree with some of the other comments here. The boxes felt excessive and completely irrelevant to the puzzles, so at the start of each level, I just pushed all the boxes into the nearest hole before starting the actual puzzle.
I really like the concept a lot and I wish more levels expanded on the red door game mechanic (e.g breaking apart the keys and reordering them for different yellow doors to unlock different paths/sections of the map in the same level). Would definitely love to play more levels of this puzzle game. Great job!