Before you ask, yes I plan on getting both games. I love the Call of Duty series equally as I do Battlefield. Call of Duty has something to offer those that play videogames addictively and sparingly, and Battlefield is starting to branch out and do the same and offer FPS fans something a little more than just being a plain, ordinary foot soldier.
Both however, play signifigantly different from one another (or at least emphasize very different ways to play). It's true BF involves more tactics than COD does, but sometimes I don't get in the mood for tactical play all the time. Sometimes, it's nice to just run wild and rack up a good score and killstreak with your personalized guns and get a good laugh. Call of Duty is built to be more FUN.
If I want to do more than shoot dudes, and communicate with a squad, then there's Battlefield. Hop in a tank and level a building, snipe someone in the brush 600 yards away, repair a vehicle, heal/revive someone; it's all meant to work as a machine (of bullets and warfare ;)) Battlefield is more REWARDING.
However, this massive dick waving competition between the two is getting annoying beyond belief from the fans and the devs side of things. Let's face it, most people weren't even fans of Battlefield AT ALL until this year or before Bad Company 2 came out. Not to mention DICE is talking about the game as if it were a COD killer when they keep forgetting both play pretty differently.
I'm not going with the "shut up and stop trolling" approach; that's just being an immature jackass. I know I'll get called out by SOMEONE on the forums for this, but rather just respect each game for what they are and have as much fun as possible when you play 'em. You can't really critique a person based on the taste of things they like to play. Both games are bound to have something that you'll enjoy. Ya never know. :)