Scrivener of Doom
Adventurer
With a small font like the 3e FRCS and 320 pages, I'm not sure you need a narrow focus!
I consider the 3e FRCS one of the best presentations of a campaign setting, especially a new edition of an existing setting, ever done. Even as someone who is not particularly a fan of FR, I was blown away by just how much that book manages to cram in.
And yet...
The fact that that book has such a density of text and such a large page count is also perhaps its biggest weakness also. There's just so much there that it can be overwhelming. I can't help but feel that a much smaller and lighter volume (actually, something like the 4e Eberron books (I don't have the 4e FR ones)) might be more approachable, if not better - what you lose in comprehensiveness, you gain in approachability.
Though maybe a "halfway house" is actually the best of both worlds - the dense, 320-page book for the dedicated fan, coupled with a 64ish page primer for the newcomer to the setting.
(I would be surprised if it was the format of the 4e books that was in any way to blame for what happened. It appears that the objection was to the content of the books, and specifically to the changes that had been wrought, and probably to the time jump more than anything else.)
My post obviously wasn't clear.
What I was describing was a product along the lines of Elminster's Guide to the Forgotten Realms to be published a year or so after the official 5E campaign setting to allow the new version of FR to settle down, as it were, and attract a fan base.
And then Ed can be unleashed to write the product he's probably wanted to write since the OGB was first published....
