Happy to hear that the difficulty was manageable . :) I found it surprisingly hard to come up with good puzzles, given the limited space (every level fits on one screen) and that there are only four different types of keys (that turned out to be a real problem for many ideas). Which hopefully excuses the somewhat steep increase in complexity after the first three levels.
I agree that this type of puzzle can become overwhelming very quickly. Would have loved implementing a function to undo the last step instead of reloading the whole level, which would make the game a bit more forgiving, but had not enough time to tackle that.
Thanks for playing!