One of my purchases at Gen Con was the Castles & Crusades Castle Keeper's Guide from the Troll Lord Games booth. Since our group is running Castles & Crusades (and has in the past), I've been waiting to pick up this tome, which was stuck in long development for what seemed like forever.
In any case, I have it now, and I'm really enjoying it. Of course, I've haven't read very far in yet, but so far it reminds me of a Dungeon Master's Guide mixed with Unearthed Arcana. It really breaks down a lot of the ideas behind Castles & Crusades, examines them, and presents you with options for your game.
Of course, it is written in that very distinct, voluminous Troll Lord prose; that's going to be a turn off to some people, but I generally like it. It gives the work a bit of character and lift.
I'm going to hold off on a full review until I'm completely done, but so far this is the sort of thing I want in an RPG Game Master's product: give me different mechanical options, help me look at the system and how it can work from my style of gaming from all angles, and give me the inspiration to make my game better. The big tests for it will be how it stacks up to the AD&D 1e DMG and the Hackmaster 4e GMG. If it can come anywhere close to the use I've squeezed out of those worthies, it will have been a purchase well made.