I finally got a copy of Castle Zagyg: The Upper Works today. Woot!
It came via Priority Mail, postmarked coincidentally on the day after I posted about not having received my copy over on the Troll Lord Games message boards.
Kudos to the Trolls for such lickety-split customer service (although a quick email saying it was on its way might have forestalled some needless heated back-and-forth). Not only do they read their own board, but they saw an irate customer [edit: okay, a VERY irate customer] and moved to rectify the problem. I must still wonder at why I never got it in the first place, but that is at least a step in the right direction.
First impressions: this thing is vast. Many books, hundreds of pages. It will take a long time to digest it all for the actual content. There are some typos and formatting problems, but not many. The maps are gorgeous, but marred by the fact that the map of the Mouths of Madness and Storerooms seems to be cut off on three sides (including completely cutting off one letter on the right that identifies one of the caves (L). Fortunately it's easy enough to figure out from context, but it's irritating that such an obvious flaw was let by.
It may sound like I'm being overly negative, and I honestly am not trying to be; the above are about the only negatives I've come across thusfar. In fact, the content, from what little I've flipped through, seems very solid. It's awesome to see some of the old Castle Greyhawk lore has been included. I don't want to spill any particular beans, but it does seem as if this will satisfy my own expectations as far as "things you'd expect to see in Castle Greyhawk" goes. I am very much looking forward to reading through the entire text, and will post a complete review once I have done so.