I love the clean layout on this. Easy to read, easy to parse, easy to run.
This feels like a missing Fafhrd & the Grey Mouser story (the early great ones, obviously).
I also like the very elegant events table.
Anyone swimming 20 feet down into sewer water absolutely deserves to find a magic item.
I love the winged vipers. A great minor Appendix N style critter. In fact, everything about this oozes sinister Appendix N vibes, down to the finest detail.
This would be particularly amazing to run with Flatland Games' Through Sunken Lands. Extraordinarily good adventure.