Gonzo ("wild & crazy") in the good sense of comic-booky and exaggerated Sword&Sorcery tropes. AFAICS the setting isn't there for logical discussion but functions as a background for gritty action-adventure with some suspense/horror elements. It has more magic and more non-human species in it than I would expect genre-wise. It happens a lot over the course of the adventure, and the characters are in for a treat.
It's very rules-light, so to speak. You can expect Mythras stat blocks and usage of the Mythras skills. If you know how to convert Mythras stats into Magic World or BRP, then you're done.
Depending on how the GM uses the module and - what's more important - how the characters will act, you can expect a lot of combat and action. The module suggests the usage of the Rabble/Underling rules from Mythras, to reflect the pulpy feel of the whole thing. If you want to use MW or BRP, you have to think about a Mook mechanic.
To get the most out of it, I wouldn't recommend grim&gritty D100 rules, where any sword attack can kill your PC instantly