The new rules for staffs and animal companions are terrific!
The improvment to feats for melee types (fighter especially) are very nice. Things like Lunge, Step Up, the Vital Strike chain, and the Critical feats will make fights much more effective.
There's many other changes I like, but those are my favorite.
With the addition of Maneuvers, we now have several different roll types for different situations.
Any time a PC or NPC wants to try a combat action that benefits from size (rather than suffers as normal attacks do), a Maneuver Roll can handle it.
Attempting to hold your ground in some kind of reverse-bull-rush? There's no rule for it, but Maneuvers can handle it. You want to Throw a medium PC into another PC? I'm not sure if there's a rule in the book for that, but a maneuver roll can handle it. Trying to hold an opponent at arms length while you fumble with something, and you want to avoid an Attack of Opportunity? Again, maneuver roll.
The best RPG rules are the ones that allow you to adjudicate improvised actions fairly, and this one fits the bill.