Thanks for your great feedback! When I first started making the game, I wanted to focus especially on the puzzle aspect, but it took me more time than I would have thought to code the entire grid system. With little time left, I decided to make it more of an exploration game. My first idea was to make a trap system, where the player could place traps to kill the boss of the room that drops the key; this was just scope creep.
Maybe next time I create a puzzle game, I should give the player the possibility to calculate the moves beforehand, to make them feel more responsible for the result.