First time I played BF1942 was with a friend on a snow day, fell in love with the game and it consumed a lot of my life for a significant period after that! Somehow shelling Midway Island with a battleship never stopped being fun... I'm also certain I invented the process of carbombing in 1942. A curious experiment with the det packs and the back of a jeep lead to probably the most satisfying way to kill tanks in the game ever. Especially when friendly fire was turned off on the server, cause you'd survive the explosion and only take minor damage from being blasted into the sky.
It got easier in later games when the det packs were made to stick to vehicles, I enjoyed the challenge of having to drive carefully to make sure the explosives didn't bounce out of the back!
Played DC pretty much from its first release to the last release. While it lacked the obvious polish of the later modern Battlefield games, in its own way, it was still more fun. Many, many, many good hours spent in DC as well as the original 1942 (I'm still waiting for a remake of El Alamein in a modern Battlefield game...). Far too much to recall, but one particular moment of good fun was a friend of mine perfecting a technique to shoot down the AC-130 with the Scud launcher (any game that actually has an AC-130 in it deserves serious commendation).
Played Battlefield 2 quite a lot as well (ended up as Master Sergeant I believe), it was fun because it was new and definitely lots of good times there, but still somehow feel like it never lived up to the original Battlefield in some ways...
Bad Company 2 was... Bad Company, a significant departure from the Battlefield series and much more of a Call of Duty "me too!" But it was fun enough, and I definitely played it a lot!
I'm still not sure if I'm going to get Battlefield 3... I don't like the whole Origin-exclusive thing, nor any of the pre order exclusive packs... but time will tell if my will can hold or not, cause the game sure looks fun...