Ghoul Keep and the Ghoul Lands isn't your typical fantasy setting. To my eyes, it feels like a darker Ravenloft.
Actually, darker might not be the right word. Grittier. It's a grittier Ravenloft.
I think it's obvious from the title that undead play a major role in this setting. They are the movers and the shakers. Humans are often the local rulers. Demihumans are extremely rare, and would only be part of adventuring parties - they would not usually intermingle with the locals. Which makes for an interesting quirk to the setting, as non-human PCs are definitely going to be sen as outcasts and not trusted by the locals.
Adventuring parties themselves need to be sponsored by, or comprised of nobles. Depending on their composition and on whose lands they are dungeon raiding, they have to give from 25% to 50% of their loot to their sponsors. As an aside, this isn't an economy based on coinage but barter, so you will often have the reverse of a normal gaming situation - instead of converting valuables to coin, the players will be seeking to convert coin into valuables. They can also get special writs of wealth issued in exchange for their new found loot (at a cost of course)
This is an extremely comprehensive setting, with nicely mapped out cities and towns, with each having enough to run a session or two in each based on the location descriptions. There are a lot of hooks to feed your players. This is very much a sandbox styled campaign setting, which is both its boon and it's curse.
As I see it, native born adventurers become "part of the system", not just by necessity to be licensed to adventure but also because they undergo the Ritual of Cleansing, which marks them and allows them to roam freely at night without fear of the undead. So, if the party is okay with adventuring in undead lands and probably running missions for undead masters at some point, all is well. If they expect to be heroes in the traditional sense, I feel the setting is stacked against them. (they are seen by the populace as heroes, but I don't see their actions necessarily being directed to "heroic acts")
It's a shame, as I really like the setting itself. It has a huge amount of roleplay potential, I just wish there was some "fighting the evil powers from within". Sure, there are some adventure seeds as such, but most of the ones that would put the heroes against the powers that be assume they are outsiders that have found (or been kidnapped) the hidden realm. Which means if they are higher level, much of the setting would be a cake walk, or low level, and the nights would just get them killed.
Maybe I wish it had more of a Midnight "rebellious" undercurrent running with it.
Still, as the author himself states near the beginning: "The Ghoul Lands setting presented in this book may not be suitable for every group, campaign, or style of play. The Labyrinth Lord is encouraged to mine these pages for any NPCs, Factions, New Monsters, New Magic Items, or story ideas that can be ported over to his own game. In addition, the awesome maps of Ghoul Keep and the various settlements, towns, and cities of Makaar Mor provided by Tim Hartin of Paratime Design can be easily restocked and reused to better fit your game world. Enjoy!"
In my opinion, Ghoul Keep is certainly worth it for the sheer "lootability" of it's contents. It's parts are just that good.