There are some hidden gems in the BF series that never got a fair shake, and they are some of my faves:
Battlefield 1942 Road to Rome and Secret Weapons of WW2 both had outstanding maps. Eagles Nest particularly stands out for me.
Battlefield 2: Special Forces city and night maps were awesome, with all the zip lining and grappling. Seems like Battlefield Hardline tried to replicate some of this stuff.
Battlefield 1943 was soooo great at the time, with its simplified take on the Pacific Theater. The planes were easy to fly, you never ran out of ammo which kept the pace on point.
Overall, though, Battlefield Bad Company 2 is the game where they seemed to hit closest to the mark on the Battlefield mass team game concept. The destructible environments, spotting mechanics, great maps, etc... easily best of the series.