I'm triggered!
BF4 has far more cheese, and DICE has become increasingly determined to cram as many gimmicks into their games as possible. UCAVs, riot shields, sraws, OP weapon pickups etc. Even BF3 needs a few things removed: the LVG (Metro was ruined when they added this), the crossbow, tugs.
I also prefer the map design in BF3. DICE got a real hard-on for skyscrapers and verticality with BF4. BF3 also has Grand Bazaar. The best map.
BF4 heavily nerfed revives (speed and health returned). This was one of the things that made BF3 great and unique. It made for some absolutely bonkers moments in BF3 where shit is hitting the fan and everybody is reviving everybody. An absolute cluster fuck. You don't get that in BF4. It also just makes for great infantry gameplay in a more competitive environment. It's one of the reasons competitive play absolutely died with BF4's release.
I believe movement is a little slower as well. Especially given that with BF4 they made jumping not speed you up. I like fast(er) paced fps games.
They also nerfed vaulting into the ground, making the movement stiff, less satisfying, and less skillful.
The gun sounds are super flat.
BF3 has squad rush. Not relevant to most people, but it's a fantastic gamemode.
Could nitpick a whole bunch of things like changes to vehicle disables or how G18 is the best sidearm, or the addition of zero'ing for snipers.
And of course, a couple of my friends think similarly and play this game. If I was to play BF4, I'd be playing by myself.
Only things I think BF4 got right was improved server tickrate, tweaked suppression and UI customization.