When trying to see how the new classes run, try running the same adventure with a mix of some of the new classes in compared to the existing ones.
Certainly there is a direct root to success that some of the more 'direct' core classes can take, but watching a group using an Alchemist and a Summoner (with one of the other players running his slightly ornery Eidolon) and short of an arcane caster with full 0-9th Spell casting was great. There were some parts that they certainly breezed but others that original (pre-APG) group barely noticed that became phenomenal challenges!
More than anything though, the new classes are full of flavour and imply their own paradigm when being played that I have always felt is sometimes lacking with variants on the core classes (its too easy to slip from failure to utility perhaps?).
I think its the diversity of the new classes I like, with everything ready to go - well done guys at Paizo! I hope the future holds even more surprises!!