I will start with a confession that I wasn't particularly looking forward to this book. In fact, the Advanced Class Guide is the first book in the hardcover rulebook line that I seriously considered not getting. This is because its basic premise doesn't really offer me anything I want or need for my games. It's not that I'm opposed to new classes. Rather, the particular classes in this book don't fill any niches that I feel needed filling.
The Advanced Class Guide introduces ten new “hybrid” classes for the Pathfinder Roleplaying Game. As hybrid classes, they combine two existing classes together, offering a selection of abilities from both classes as well as new abilities that fit their combined flavour. These classes essentially provide a way of multiclassing without multiclassing. This is the fundamental reason why these classes mostly don't appeal to me. While they do have some new abilities, they don't offer any new flavour. In all cases, it's possible to create characters in the same style with the existing multiclass rules. Now, I should probably also confess that I like the multiclassing rules. Yes, there are problems with them (particularly with multiclass spellcasters), but as long as you can get away from the idea that “class” is synonymous with “profession”, you can create a huge variety of character types with them—and yes, they can even be effective characters. As there is already a way to combine the abilities of different classes, there really doesn't seem to be a place for hybrid classes. New classes should be exactly that—new. I have the same problem with the magus from Ultimate Magic, to be honest.
As well as multiclassing, the game also uses archetypes as a way of providing characters with a smattering of abilities from other classes. Archetypes provide ways to create characters that are just slight variants of existing classes, so that an entirely new class isn't necessary. The new classes in the Advanced Class Guide feel a lot like archetypes in many ways. In fact, in the original playtest document, they were alternate classes of both their parent classes. (Alternate classes are archetypes that change a large number of things about their parent class and so get a complete write-up while not being actual new classes.) However, this was changed in the final book, so they are now fully separate classes. I personally liked them better as alternate classes—though, honestly, even as alternate classes, these classes still felt mostly unnecessary.
Nevertheless, despite my misgivings, I did decide to get the book, feeling that there would likely be other parts of the book (like new feats and spells) that would be useful to me, and—who knows?—I might even decide that I like the new classes after all. Alas, it didn't quite work out that way. I'm not saying that the Advanced Class Guide is a bad book. It does what it set out to do, and it does it pretty well. It's just going to see very little use in my games. I might use the swashbuckler and shaman, though.
All that said, let's take a look at what it has to offer and examine both its strengths and its weaknesses.