I generally find that some FATE worlds do it for me, and some don't, but just about every FATE world has something that I can borrow (steal?) for my game.
"Grimoire" was a pleasant surprise, all the way around. There isn't anything about this setting that I didn't like. Recognizing, though, that not everyone shares my exact tastes, here's a quick review. Yes, I'm a fan of this one, but I hope my review will suffice to let you know if "Grimoire" will do it for you-- or if it won't.
The most interesting mechanical twist in "Grimoire" is that it provides an entirely new spin on magic for FATE Core! If you're of a certain age (read: 'old'), you might remember the Eternal Champions line of fantasy roleplaying games by Chaosium, "Stormbringer" and "Hawkmoon," both based upon the fiction of Michael Moorecock. What set these games apart (mumble mumble, handwave) years ago is that their magic system was entirely based upon summoning extraplanar entities, beings which were generally much more powerful than the player characters, and then either bargaining with them or magically compelling them to serve you. This form of sorcery was dangerous, often as dangerous as anything else in the game, and that danger factor resulted in immensely powerful characters who were often doomed for dabbling in dark forces which they couldn't entirely control (mwaaa-hwaaa-haaaa, sinister laugh, and CUT!, fade to black).
Well, the magic system in "Grimoire" is a lot like that. Here, of course, the entities in question are reflected by Aspects, rather than a series of godlike numbers which dwarf the characters' own attribute ratings, making the imbalance of power between summonee and summoner a bit less daunting... at first. You see, "Grimoire" also introduces rules for 'indebtedness' to these malignant entities, so while the astral bugaboos that you summoned for protection might or might not pose a dire risk to you at the very outset, calling upon them for additional services does give them a bit of added leverage over you. These beings are a form of immense power, bottled up in your back pocket, which you hope to be able to use sparingly, if at all, all the while remaining mindful that the imbalance of power which leans in your favor today could shift away from you at almost any given time once you let the genie out of the bottle.
Honestly, you could port these rules over to any fantasy setting and have a complete magical system, ready-to-run, as long as you aren't hung up on the idea that magic = spells. If that's your thing, or if you want a magic system where the players have a more primary role in creating magical effects (as oppsed to the more secondary, behind-the-scenes role of conjuring and attempting to compel the entities which fill that more primary magical role), "Grimoire" might not be for you.
Setting-wise, the game does what it needs to do. Player characters are warlocks, capable of summoning daemons, malignant extraplanar entities, and that makes them valuable assets for the rich and powerful. A few factions are detailed in somewhat cursory manner, several places are described, and a couple of NPCs are identified. This should be more than enough background info for most FATE GMs to jump into. Character creation rules are suitably modified to support the rules for warlock magic and to support the setting presented.
Really, the meat of "Grimoire" is its unique magic system, which fully delivers upon its particular concept of how magic works in this game. The focus of this world is 100% about warlocks, who serve as a weapon in the arsenal of a powerful elite. You won't find elves or dwarves here, although of course it'd be a simple matter to Aspect some up if that's your thing. If you're looking for a dungeon crawl, or want something with an old-school D&D feel to it, I'd suggest the FATE Freeport Companion. But if you want a refreshingly different type of fantasy game-- one where magic is dark, mysterious, unpredictable, menacing, and more than a little dangerous-- this is a nifty little FATE world which stands tall on its own merits.