Even as a long-time IF fan, Hadean Lands blew my mind. It remembers exactly how you solved every puzzle, so if for instance you find a door locked again after y

Even as a long-time IF fan, Hadean Lands blew my mind. It remembers exactly how you solved every puzzle, so if for instance you find a door locked again after you figured out how to unlock it, all you have to do is say you want to open the door and the game replays the whole process of unlocking it (to make up an example so as to avoid spoiling anything). Some of the puzzles get quite involved, so the depth of the system's memory is quite impressive. Also the symbolic way it handles alchemy, such that objects are understood to be aligned with various planets or aromas, allowing you to get creative with alchemical recipes, is probably the closest I've seen to "real" alchemy.