In the very early 1980s, contemporary D&D modules typically troubled themselves with story lines only long enough to get you underground; once you were in the dungeon, you slogged through hours of room-to-room combat and hidden pitfalls. The only thinking required was "How do I kill this thing?" Sure that was fun for a while, but this adventure illustrated that our gaming brethren in the UK were taking D&D to a more sophisticated level. This is definitely a thinking player's (and DM's) adventure with clues to be digested and a plot to be figured out; it gets high marks for innovation.
That said, the adventure is actually somewhat lacking in many ways. Yes, it lays out a plot with a twist or two, but the secret is not really very sinister, or even that well concealed. The "dungeon" portion of the adventure, including encounter descriptions, maps, and NPCs are uninspired and the designers really left far too much up to the DM. What you get are reminders that the DM will have to develop so-and-so NPCs and encounters or come up with this-or-that villain strategy just when you're hoping that they'll give you something meaty to dig your creativity into. It seems to be a lot to lay on a person who spent $6.50 of their hard-earned paper route money to play this adventure back in 1982; especially considering that at least 4 pages of this module were wasted on full page illustrations and useless visual aids. Still, if the DM is willing and able to flesh this thing out, it should lead to one of the better D&D experiences from that era.