Best of luck with your revisiting the system. For me, 3.x/PF1 is the one edition that I would never want to play or DM again.
- Diagonal movement
- Ticking off individual boxes (and "half boxes" for untrained) skill proficiencies
- Grappling, tripping, disarming, swallow hole, and other combat maneuvers
- Flat-footed, touch, and regular ACs
- Magic item Christmas trees
- Buff smorgasbords before combats
In terms of Pathfinder (1st edition)
* I'm not sure how Pathfinder handles diagonal movement, since we use Theatre of the Mind
*That's not how skills work in Pathfinder (1 skill point = 1 skill rank, you get a flat +3 if it's a trained skill)
*Pathfinder changed how combat manoeuvres work, which greatly reduces the cognitive load on the GM - although stuff like feinting still has its own sub-system
*Pathfinder is the same; it's not an issue from the player side (write the numbers on your character sheet) and the Bestiaries give the GM numbers for all of the monsters, so it doesn't add to the GM's workload, and gives lots more tactical options (the heavily armoured tank might laugh at most encounters but won't fancy taking on a bunch of shadows)
*Pathfinder Unchained gives you an alternative "inherent bonus" system you can use instead
*I consider this to be a feature, not a bug, as it is part of the game's tactical element; I assume you are approaching this from the DMs perspective (if you don't like it as a player, then I guess you can just ... not do it?) in which case you can make sure the PCs don't always get time to prepare, or aren't always aware of the right thing to prepare, or blow a load of spell-slots against a weak opponent
I appreciate I'm biased (I enjoy playing Pathfinder) but from my perspective many of the issues people had with 3.5 were fixed by it.
The use of archetypes also largely removed the appeal of prestige classes, and allowed character customisation without the need to plan way in advance. The absence of archetypes is probably the main reason why I'd hate to go back to 3.5 (although the racial substitution levels did introduce that in a small way).
The second thing I really like about Pathfinder is traits, which allowed a further amount of customisation - if you really want your Fighter to have Use Magic Device as a class skill, then you can. Obviously, they are one more thing that can be abused, but that brings me back to the original point - if you don't want a broken game, then don't break it.
Now that it's officially "over", with no more "First Party" content being made, I've started looking at Pathfinder 1st edition as more of a toolbox, in which you select the elements you want to have in your games and exclude the rest. The GM is excited to run a "World of X" campaign, the players are attracted by the GM's enthusiasm, and come up with World of X characters. Anyone with "World of Y" character ideas will have to wait for the next campaign so see them in action.