While in no way perfect, Pathfinder does prove to be a very well thought out and well balanced continuation of the D&D 3.5 ruleset. Each class feels unique and useful, and much more balanced than in 3.5.
The Core Rulebook also has some very useful resources usually reserved for a Game Master's guide in it, making it almost 2 books in 1 at nearly 600 pages, and a great starting point if you want to get into the game.