Ill Met in Lankhmar is a novella in the guise of a Neverwinter Nights module. Designed as an ode to Fritz Leiber's classic story of Fafhrd and the Gray Mouser, playing this module allows you to experience the story. If you enter the module with that understanding, it makes the whole thing work a lot better.
I haven't had the pleasure of reading the original story, but I've added it to my to-read list on goodreads as a result of playing this module. The writing is witty--almost to a fault, but not quite. While the adventure takes on a dark tone as the story progresses, the style of the dialog, in particular, is whimsical and delightfully engaging. I'm guessing that the vast majority of the writing came directly from the book, and I think the zeal of the module's author for the source material comes through in spades.
The areas are extremely well designed, with lots of little flourishes to enhance the experience. The city streets are filled with a kind of unhealthy smog, for example, and the player character of Fafhrd is rendered larger than life using custom content.
The main critique is that this module is probably the most linear that I've ever seen. There are a handful of optional interactions, including a few stops at merchants, but that's it. There is a ton of dialog, and there were times when nearly 30 minutes went by as we moved from cutscene to cutscene. I was just trying to get to the next down moment so that I could save, and the result was a late night. That all said, it was a neat experience. I enjoyed playing the module, and especially meeting these characters who have so far not caught my eye.