It inserted well into my ongoing Eberron game, so I'm using it immediatly.
I'm undecided on the Delve format, on one hand everything is there, but it also seems like a lot of wasted space. Hopefully not every encounter in every adventure needs a Tactical Spread, or the page counts will be horrible. I'd also have liked references for some of the monsters as to where they may have originally appeared, or if they're original to the adventure.
I still miss boxed sets though, having the Tactical Spreads in a book, and the core stuff in a book, with removable maps, that would be the best.This does seem the perfect format for web-enhancement though, particularly if Player Versions of the tactical maps were available.
As far as plot changes, I'll be cutting it a bit, so won't be using the Fanes, and might trim a bit more, plus accentuating some other things that are more of a sidebar to fit into my campaign, but I really do like the idea. I am the Ancient, I am the Land has real meaning.
Though no chest with hiding place with Deck of Many Things.
Bonus Stuff: Legacy Items are great, Knight of the Raven is great, Lightbearer stuff cool enough. Magic Items are generally good, though the format still irks me as wasteful.
The only big thing that bugged me, was the constant reprinting of Strahds stats wherever he MIGHT be. It got tedious after a while, especially given the size of the stat block. Otherwise all is good, and I look forward to Madam Eva.
