EA's Product Manager, Kevin O'Leary in a Battlefield 3 interview: Why Battlefield 3 doesn't want to be in direct competition with MW3, why it's different, and why he thinks BF3 will win the war this fall.
"The important thing to note here is that Battlefield 3 is staying true to it's Battlefield roots and adding bits and pieces to draw in more players. Some of these pieces are big, such as the powerful Frostbite 2.0 engine which brings some of the best graphics and physics to a modern day game. BF3 wants to draw people in with the fact that Battlefield is about choices, "We give you so many tools; you can choose your vehicles, your weapons, your class." This choice style game play has been the foundation of the series and is evident on the Battlefield 1942 game case.
The online play is also very different between the two and has always been. Call of Duty is about running and gunning. I want to make it clear that the Battlefield series also has this, but it also has a strategical side as well. In Battlefield 2 you can find a full 64 man Strike at Karkand server, 32 people shooting at another 32 people at very close range. You can also join another server with 64 people on a map such as Kubra Dam where there's a USMC squad sneaking along the outskirts to steal the MEC's airfield base, making the MEC's advance a bit more difficult. Battlefield 3 is NOT trying to be Modern Warfare 3, it doesn't have to be. It has everything that MW3 will have, plus more. If you want to run and gun, you can do that, if you want to guide your team to victory through strategy, you can do that.
Most players buy into the Call of Duty series, because all their friends are doing the same thing. Battlefield 3 hopes to win over the followers, the people who buy the game because everyone else is. The people who are on the fence between the two games are also on EA's target list. Hoping to win them over with BF3's impressive graphics, animation, story line, destruction, and customizability.
[...]the people who buy a game because it's hugely popular or because their friends bought it, not necessarily because it is the best option."