Thanks for the review and the feedback! I put a bit of thought into how to introduce the various mechanics without needing a tutorial so I am right chuffed that you noticed and liked the difficulty curve.
I totally get where you're coming from with the monster sounds, I think I need something longer to get more variation and less interference between the different monsters. Trying to keep the levels short enough that redoing them doesn't feel too onerous while still allowing the puzzles to be interesting and not advertise the solution by always putting the key right next to the lock is... hard. I'll try to think of a way to tweak Thief in particular.