So here is a quick rundown of the table of contents which gives a pretty good idea of what's in the book.
D&D and the Birth of a New Edition (2 pages)
The Process of Re-Cration (4 pages)
Sections about reimagining monsters for 4e
The Setting of D&D (4 pages)
Sections about the Points of Light setting, and how it came about
The New Cosmology (2 pages)
Sections about an overview of the new cosmology and the end of the great wheel
The World (8 pages)
Includes sections Fallen Empires, Locations of Note, The End of Human Dominion
Dragons (6 pages)
Giants (2 pages)
The Underdark (4 pages)
The Feywild (8 pages)
The ShadowFell (8 pages)
Art Gallery (1 page)
The Elemental Chaos (12 pages)
Includes sections on Elementals, Locations of Note, and the Abyss
The Astral Sea (10 pages)
Includes sections on The Gods, Angels, Devils
The Far Realm (6 pages)
Sections on Aberrant Creatures and Mind Flayers
Staff Thoughts on 4th Edition (13 pages)
Sections about... lots of things
The Next Word (1 page)
A few words about what's coming