Zork I sets the standard for adventure games. You are free to explore the Great Underground Empire in your own fashion, making it truly feel like exploring. One of the strengths of Zork is its sense of fun. It plays with allusions, but without getting too silly.
Your mission in Zork is to explore the modern remains of what was once a great, underground, magic empire; i.e., the ruins of what was once a typical fantasy setting. You must collect treasures and survive.
The weakness of Zork I is its story and background. There is little more than greed to propel you through the dungeon: collect treasures for fun and profit. The characters you encounter have no depth, and the settings are just there to challenge you. These were small considerations when Zork was first released, but they date the game from the perspective of "interactive fiction".
Solution by me.