Player
New players, here is what you should read to play - comes out to less than 50 pages.
Core Guide
Character Builder
Armor and Gear - first 3 pages
Wizard Spells (First Castings) - first 4 pages
Cleric Spells (Sacred Beginnings) - first 4 pages
OD Cheat Sheets
GMs and DMs
New GMs and DMs to become a Dungeon Narrator, here is what you should read to play - comes out to less than 80 pages.
Core Guide
Character Builder
DN Guide
Armor and Gear - first 3 pages
Monster Trove (First Encounters) - up to page 6
Wizard Spells (First Castings) - first 4 pages
Cleric Spells (Sacred Beginnings) - first 4 pages
Magic Items (First Discoveries) - first 3 pages
OD Cheat Sheets