Just picked up my copy at the local games store last night. As an old 2nd Edition player, I can hardly put into words how happy I am with the Pathfinder Core Rules. When a group of friends and I decided to start up an online campaign earlier this year, we all assumed that 4th Edition would be as good a rule set as any to go with. Boy were we wrong. If we wanted it to feel as though we were playing a computer game, we would have saved some time and met up in the World of Warcraft :P
This book's presentation is spectacular, the rules are sensibly organized (there's even an index) and there's a real sense that they've been written with actual players in mind. Pathfinder is a breath of fresh air -- I once again feel I have the freedom to tailor rules to meet the needs of my players and campaign. In short: thanks Paizo!
I'm sure I'll be chiming in on a number of other threads here on the site. I've got a lot of questions about the various Pathfinder products...