I think it's the weakest one out of the Special series. I'm not the biggest fan of those modules to be fair, but this one somewhat lacked pacing more than the other. I needed some breathing room, as in literal rooms (or part of the caverns) that were not populated by a) monsters or b) dangerous wildlife or fungi. 

I don't mind that as much in Tomb, maybe because it was constructed from A to Z, instead of a series of caverns, which would have it's own microcosm on top of the stuff added by the mastermind hiding treasures inside. Mind you, there's some beasts, animals and fungi that coexists, but it's small pockets of 2-3. I'm not into the intricate setting of the last room either. The last few sentence regarding PC leveling, mediocrity of play and how those reflect on the DM was ew.

As a DM, the stuff that I would lift from this and use elsewhere are the diagrams at the end, maybe the magical boat, and that teleportation in different alternate location with a possible puzzle to go back to the place you came from.

As a player, I don't think I would like this module at all. Other than the difficulty of it all, I would feel like I have a hard time staying motivated to get through it.