Having just finished reading the Pathfinder RPG core book, what I've been wondering about is if there is still sufficient incentive to take levels in a prestige class.
Imho, the base classes have received so many power-ups, I'd have a hard time justifying taking a level in a different (prestige) class.
Or is it just the prestige classes in the core book that aren't particularly attractive?
Or am I just overlooking something that makes them more attractive?
Depends on the prestige class.
Frankly, if you're trying to eke out the most powerful build, you're STILL going to be taking prestige classes out the wazoo since the most powerful/broken PrC are STILL broken/powerful and they weren't taking the flavour PrC anyway.
For example, if your players are power-gamers, nobody was taking any spellcasting PrC that had more than 1 non-increasing spell level feature per 5 levels of the PrC. However, if they were the type to use Incantrix and IotSV in their wizard builds, they're STILL going to be (ab)using them.
What Pathfinder has done is that many of the more, I guess, tamed PrC were either invalidated by the single class options or actually have become weaker.
What a lot of people forget is that most PrC pretty much blew chunks in terms of power and only I'd say about 10% of all the PrC were actually truly broken (Planar Shepherd is STILL massively broken).
One of the side effects of the PF change to shapeshifting for druids is that it actually makes druid PrC actually more attractive than before. Previously, there aren't that many druid PrC that actually increased both spellcasting and shapeshifting at the same time and since both features were so powerful, it meant that the BEST build for druid was DRUID 20.
With the nerfs to shapeshifting, people might actually look at the druid PrC now.