Hey now, can't have BF go back in time just yet, they still need their near future kick. I personally loved BF2142 but partially because I played on a server with forced team play. (Listen to squad/commander) Way more intense and fun than usual roaming clusterfuck that is bf4. Never liked air carrier assault, but regular objectives. Probably OP, but loved doing the air transport with a bunch of engineers.
Return to WW2 with a lot more obscure vehicles that the public isn't aware of would be great. Maybe with a lack of helicopters also make the game a little more heavily ground vehicle focused. My biggest issue with return to old is from a pseudo RPG or whatever you call it aspect, I think most people are addicted to being able to mod out weapons. And back then you basically was stuck with irons, or a rickety old etched glass scope....