Wow, this game is so fun. Thoroughly enjoyed every level in both castles. And the music is amazing too, simple but really enjoyable. Good job making it yourself. Also love the double theme take.
Regarding difficulty, I think you got the difficulty curve right, at no point I felt frustrated. There were a couple levels were the solution was really simple, but I guess that's not an issue.
Castle 2 specifically was a cool twist on everything before, though I feel like canons kinda trivialize many puzzles, and that action counter stops mattering as much once they are in a level. (Btw thanks for allowing to press space to fast-forward a canon)
A nice addition to the game would be to allow to scroll through the level as you're playing. This would be especially useful if you're currently in a canon and want to look around before deciding on the next move.
Lastly I did have technical issues, specifically the game seems to not work at all on Firefox. The game just shows a blue screen and I can't play. Had to switch to chrome to play