It's notable that the whole point of the Pathfinder RPG was to tweak the 3.5 system but allow players to continue using their supplements from 3.x D&D. Now, basically this means that 3.x material is PF material, which essentially gives Pathfinder an out of the gate start with high amounts of supplementary material.
They even rebalanced the core classes (how well varies) to make them more in line with options provided in 3.5 splat-books, so that there are reasons to go into higher levels of base classes without prestige-classing out of them. Such adjustments were intended to make characters who didn't multi-class a lot, or those without a lot of prestige classes, just as viable. They also gave a face-lift to the existing OGL prestige classes (Arcane Archer, Arcane Trickster, etc) which made them a bit nicer as well.
Really, the best advice would be to check it out and see what you think. If you're a fan of 3.x, then much of it will feel familiar and nice. If you're expecting it to be identical to 3.x, then you will be disappointed. If you're expecting it to be a completely different experience, then you will also be disappointed.
I found it pretty nice though, and currently am playing in a 3.x/Pathfinder hybrid with other options, and a few extra house-rules (I like tinkering with the system and consider myself something of a game-designer).
I'm particularly fond of PF's skill system which is simple and elegant. To sum it up quickly: You have a rank limit equal to your HD in any skill. If that skill is a class skill for one of your classes you receive a +3 bonus to that skill. This means at low levels a rogue could have a +4 bonus to stealth, while the fighter could have a +1. However, the fighter could eventually reach a +20 bonus at 20th level, where the +23 the rogue has isn't as large an advantage. I like this because it allows more diverse characters without the need to multi-class a lot, while it keeps skills associated with different classes.