This classic game is exceptionally well-written and implemented, together with a well-done hint system.
The game features a pretty small playing area that is packed with objects and several NPCs that take interesting actions.
The game is hard, and I had to rely on hints much of the time. The puzzles require creative uses of a large number of objects gathered from different areas, and some large leaps of intuition.
The plot is about the nature of reality, and it has several mind-benders, which is why I am not describing it as much.