1) Multi-classing is a big issue with certain players who are always max-min'ing. Had a player character who was a halfling - level 2 paladin, level 3 ranger (hooded champion), level 5 sorcerer, level 10 arcane archer... had saves, perception, panache, spells, etc. was insane. He started the campaign after level 1 so picked classes like a catalog without having to play those levels....
2) Small character size bonuses too big compared to penalties. Better AC, better to hit, smaller weapon crit ranges (scimitar, kukri) are better. Who cares that the weapon only does 1d6 instead of 1d8 when you crit on a 15. The damage comes from the bonuses.
2a) Speaking of sizes.... there is no real benefit of wielding larger weapons. Their damage increase is nominal compared to their faster, higher crit counter parts. Tired of seeing jacked fighters in full plate wading into battle wielding toothpicks....
3) Skills outta hand.... said paladin in point 1 above was like +45 on perception checks (at like level 12). Made the rogue obsolete when finding traps. Plus, no creature, secret door, trap, or anything could be hidden. I for one don't want to turn into a big cheese by jacking up trap DC's to 60, but very difficult to offer surprises or challenges other than hack slash.
4) Keep the race limitations... i.e. arcane archers should just be elven
5) Stop with the ridiculously low cost powerful magic items. Boots of the Earth.. market value 5,000gp... provides infinite healing when you stand still.... eliminating healers and promotes "Guys, can I just stand here for 5 minutes so I can heal?" There are so many magic items out there, it is tough to regulate them. I don't wanna be one of those tyrannical GM's that has to approve every item.
6) Revamp the magic item system as well for towns.
7) I read there was a complaint for range fighters with arrow consumption. Range fighters get full attacks way more often than melee fighters who have to move in a fight. Their only buffer (minus the ridiculous low cost of an efficient quiver: 1,800gp) is that when you shoot 6 arrows/round, you are going to have to be wary of your arrow consumption. Not sure what the fix is other than spending money on magical alterations to weapons...
8) Attacking from the ground.... Rather than my PC's taking an action to stand-up (and suffering an attack of opportunity) after being knocked down by a dragon or a giant, they choose to fight from the ground.... their attack bonuses are so high that the AC's of the monsters are not an issue (again, unless I jack em up). Must look ridiculous seeing a fighter swinging his greatsword while doing the worm on the ground....
I am sure I will think of more. I do thoroughly enjoy the game. Not sure I feel like converting to PF 2.0 since I own a majority of the books already. Maybe I'll just adapt some of their changes...