This is the one that has it all - dungeons AND dragons.
This module has really well fleshed out and interesting NPCs. The social interaction and investigation is engaging. Running this the first time is definitely in my top 5 memorable D&D moments of all time. Players still talk about this one - remember to never stand in a line when charging a black dragon!
Builds extremely well off of the setup of the previous adventure, and it contributes to a vibrant understanding of Phlan as a city. Could be worth picking up and running just for being able to add the treasure as part of your DM rewards, but is an outstanding example of what great adventure writing can look like as well. Great pacing - gradual buildup leads to an explosive climax.
[5 of 5 Stars!]