Brilliant! Baffling! Bizarre! Utterly confounding. Just the most amazing coagulation of weirdness I've seen in a long time.
Perhaps the best thing about it is the complete lack of predictable OSR vermin. Not a Goblin Fight to be seen! EVERYthing is nonstandard, unique, or just too damn strange to be dealt with the Usual Way.
Unique creatures, civilizations, and locales.
Makes for incredible fun just reading. MUST find out how it runs.
While the presentation leans toward the gonzo and humorously bizarre, it would be very, very easy to run it with a darker than darkly dark grim Lovecraftian tone.
I want to see more of this Underground setting. I want to send Player Characters drifting on the Black Ooze River on an ill-advised mission of Corsair mayhem. I can barely wait to write my own adventures in this setting, after enough tasty beverages to get into the appropriate mind-set.
In short... I have to kind of recommend it. Lots of fun with endless applications.
ALL HAIL SHAGGATH KA THE WORM SULTAN.
[5 of 5 Stars!]