A flavourful module of the Underdark, featuring some of adventurers' worst nightmares. You can tell an excellent story with adventurers through their encounters in the den and it should keep them on their toes and leave them some lasting memories. However, there remain some undesirable portions, such as trying to figure the motivation of the final boss, and wondering why he would not be any more intelligent given his species.

To really draw out the story potential, the DM would have to spend some time to research the lore of the mind flayers and be creative with how to run the final boss encounter. Assuming you're not there to totally murder the adventurers, try to prevent save-or-die scenarios and give the adventurers a real chance to save themselves.

(One point to note - a consumed brain would mean adventurers need access to Resurrection or Reincarnation to continue playing their characters, both options not likely available at their levels).