Hmm. It mostly seems to be a handful of different design philosophies from 3.x.
> There is a minimum HD Based on your BAB (d6 for 1/2 bab, d8 for 3/4, d10 for 1/1).
> Nothing Costs XP.
> Many game mechanics work slightly differently (though its all readily indexed and easily searchable on d20pfsrd.com)
> No dead levels.
> When guaging the power of an option, "Core is King" IE balance your options against the corebook, not against the entirety of the PF line. Its supposed to reduce power creep.
> Prestige Classes are for specific and unusual builds, not for normal builds. Generally things like joining a specific mage guild or the pathfinder society etc. Pretty much no generic Prestige classes (there are a couple to allow for effective multiclassing when the multiclass rules would give you a crap character otherwise, along the lines of Mystic Theurge).
> Instead of Prestige classes, you're encouraged to stick to base classes, and they reward staying in one class all the way up. They added archetypes (swap out X class abilities for X alternate class abilities.)
> Slight increase in the power of player races.
> and the Guidelines for Monster CRs are given in Bestiary 1. there's a big table. Its not as specific as I'd like, but its much better at pegging CRs than the wotc method of pick a number, playtest, pick a new number.
> Few things are immune to sneak attack or critical hits now.
Thats most of the stuff, other than lots of little changes, like how X feat works or something.