It's Big! Massive actually. Course it is the Player's Handbook and the DMG combined. I haven't really had time to do much more than scan it. Production-wise it is a beautiful book. I've always loved Wayne Reynolds art. That was one of my many disappointments with 4E (the art) for me. Layout is nice. Like I said I have really only been able to scan through it and read tid bits here and there. My wife wanted to know about Necromancers and Half-Orcs (I love that woman!), we both liked what they did with Half-Orcs, and she and I both loved the Sorcerer blood-lines (Undead blood-line cool!). I like the changes to the Cleric. Glad they dropped Rage Points from the barbarian. Not sure how I feel about them using Monk Ki points.
All in all I see lots of options for players! You can really tweak your character with these rules.
I think it is safe to say if you didn't like 3.x you won't like these rules. Pathfinder lives up to it's roots, it is clearly strongly tied to 3.x. But they have added some really nice changes to it.
If you liked 3.x I think you will enjoy this book, even if it is just to houserule some of the stuff from it for your 3.5 Campaign.