This is largely a book of rules updates labelled 'Player's Guide' because it's a more appealing title. As a Realms fan, I'd like to have the bits of actual new material (the planar information, the timeline update), but the book doesn't have much to excite me to spend all that money. (The new Thames & Hudson book on the art of the Picts looks more interesting.) An actual Realms player's guide (with lore players in a Realms campaign should know) I'd get, no question.
For someone who doesn't use the Realms, I don't think (not having seen it) the book is much less campaign-neutral than a 'generic' title set in an implicit setting that just doesn't have a name, history or context.