Duncan Stevens posted an excellent review of this ultimately disappointing underdog from Infocom in SPAG, so I'd like to quote it here in full: "The original Zork series was...

Zork: The Undiscovered Underground is a fun Zork game designed by ex-Infocom designers Michael Berlyn and Marc Blank, released as freeware to promote the release of Zork: Grand Inquisitor.

Although subtitled ?A Text Adventure Game,? Zyll is actually a revolutionary text-only RPG that introduces many concepts that have not since been seen together in one game.