When is a text adventure game not a text adventure game? When it's Beyond Zork: The Coconut of Quendor.
Infocom's fourth entry in the Zork series (actually the 8th if you count the related Enchanter series and Wishbringer) combined interactive fiction with light RPG elements such as equipment, stat sheets, an on-screen map, and character leveling to create a unique game that may be best compared to a single player MUD (a SUD?).
Beyond Zork sports procedurally generated maps in some areas, so replay value is theoretically infinite. But randomness is a double-edged sword in this case: its magic items move around between saves and loads, and that can frustratingly break the suspension of disbelief (i.e. you see it, you die, you come back, and it's gone). Still, Beyond Zork is an amazing game that deserves more attention than it usually gets.
Discussion Topic of the Week: What's your favorite entry in the Zork series? Every Zork-related game counts.