spoiler alert This is a nice module, well suited for 1st level characters. The conflict between the kobolds and goblins gives for the characters to explore the dungeon without needing to kill everyone if they do not mind allying with the kobolds. There are enough details to help a GM develop the area around the Sunless Citadel, but the content of the adventure is really about the dungeon. I have but two complaints concerning this book:
1) Cutting down the Gulthias tree kills the supplicant under its influence. It would have nice to alter this and add a way that supplicants can survive and be redeemed with an atonement spell or with any other quest. It would have allowed for further development for this adventure.
2) I think the village of Oakhurst could have been a bit more developed. There are notes about the village, but a couple of sidequests idea related to the main adventure goal would have been nice. After all, the "bad guys" are not confined to the dungeon.
Otherwise, this is a nice first adventure and it is easily converted to any campaign.