Ironically, it looks like there isn't anything in the new stuff that's half as much fun to argue about as sorcerer bonus spells known.
Alternate favored class bonuses aside (though, honestly, I'd much rather complain about how bad the elven wizard bonus is, and how much of an auto-take the gnome bard one is), it's the alternate class builds mentioned in today's preview that I'm most excited about. Several classic archetypes - and some former 3.5 PrCs, too - finally getting some Pathfinder crunch! It's like Christmas in August!
Reprinting from the Paizo thread, here's the Big List o' Class Variants in the APG:
Barbarian: Breaker, Brutal Pugilist, Drunken Brute, Elemental Kin, Hurler, Invulnerable Rager, Mounted Fury, Savage Barbarian, Superstitious, Totem Warrior
AND new rage powers
Bard: Arcane Duelist, Archivist, Court Bard, Detective, Magician, Sandman, Savage Skald, Sea Singer, Street Performer
Cleric: Subdomains*
Druid: Aquatic Druid, Arctic Druid, Blight Druid, Cave Druid, Desert Druid, Jungle Druid, Mountain Druid, Plains Druid, Swamp Druid, Urban Druid.
OR
Bear Shaman, Eagle Shaman, Lion Shaman, Serpent Shaman, Wolf Shaman
Fighter: Archer, Crossbowman, Freehand Fighter, Mobile Fighter, Phalanx Soldier, Polearm Master, Roughrider, Savage Warrior, Shielded Fighter, Two Handed Fighter, Two Weapon Warrior, Weapon Master
Monk: Drunken Master, Hungry Ghost Monk, Ki Mystic, Monk of the Empty Hand, Monk of the Four Winds, Monk of the Healing Hand, Monk of the Lotus, Monk of the Sacred Mountain, Weapon Adept, Zen Archer
Paladin: Divine Defender, Hospitaler, Sacred Servant, Shining Knight, Undead Scourge, Warrior of the Holy Light
OR
Antipaladin
Ranger: Beast Master, Guide, Horse Lord, Infiltrator, Shapeshifter, Skirmisher, Spirit Ranger, Urban Ranger
AND new combat styles
Rogue: Acrobat, Burglar, Cutpurse, Investigator, Poisoner, Rake, Scout, Sniper, Spy, Swashbuckler, Thug, Trapsmith
AND new rogue talents and advanced talents.
Sorceror: Aquatic Bloodline, Boreal Bloodline, Deepearth Bloodline, Dreamspun Bloodline, Protean Bloodline, Serpentine Bloodline, Shadow Bloodline, Stormborn Bloodline, Verdant Bloodline
Wizard: Elemental Schools and Focused Schools
*subdomains are domain variants - i.e., "Fate" instead of "Luck" - that can be taken in place of the regular domain for clerics of gods who offer the regular domain. Each modifies the domain spells and changes one of the granted powers of the regular domain.