As much as I enjoyed 3rd Edition (or more accurately, 3.5 and Pathfinder), there were a couple of rules and mechanics that bugged.
First and foremost, Spell Resistance. I hated it. Mostly because it seemed to climb at a faster rate than the Caster Level Check to overcome it. No matter how many feats I took or whatever things I did to boost my chances at beating SR, time and time again I hear Crwth say, "Sorry. Your bad ass spell fails to get past it's spell resistance." I wanted to punch him in the face. A lot.
Next on my list of 3E peeves was the way skill ranks and the various bonuses tended to make doing the impossible into the trivial. With a decent INT modifier or a few feats and/or a bit of focus on a couple of skills, and it wouldn't be long before beating a DC 20 was only a matter of not rolling a natural 1. Rogues were the worst with the insane number of ranks they had to spend every level. By the time they hit their teens in terms of level, they can tumble across a football field covered in razor blades and not get a scratch.
Finally, dinosaurs. Why the hell does a fantasy game need stats for dinosaurs?
Anyways, while I'm mildly disappointed that dinosaurs have reared their extinct heads in the playtest Bestiary (yeah, I skimmed it), I am loving that all the checks and saves seem to go back to the character's six core stats. Those stats that go up maybe one point one at time every four levels; barring magic items and temporary boosts from spells.
Seriously, whoever came up with that idea deserves a big fat raise and a freshly baked cookie on their desk every morning.