Holy thread revival!
BFBC2 was good, but I don't agree it's necessarily the best.
The problem is that for each BF, DICE gives with one hand and takes with another. IMO BC2, BF3, BF4 and BF1 all have something which makes them better in some regard, but none have it all..
The destruction and map design (for rush at least) in BC2 is superb. Balance between air and ground*, lack of prone, and no strafe run is not so hot. And it doesn't integrate with the origin on battlelog friends lists.
*After the slowed down the dart it became very difficult to hit a good heli pilot.
Vietnam expansion was epic fun, but last time i looked, I could find vanilla servers but no one playing vietnam.
Edit: Also the gun balance wasn't great, if you had worked out how to use the AN-94, you won..
(2 rounds, in one spot, and capable of breaching the supposed RPM by fast clicking..)
It was certainly a blast to play at the time.