IMO, it's still too early to tell if BF3 is going to supplant the CoD series. Whether it's been by choice or lack thereof, CoD has been the king of mountain when it comes to FPS for a while now and one trailer isn't enough to knock it off its well-deserved pedestal.
I'll admit, the early screenshot and gameplay videos of BF3 are AMAZING, but keep in mind that these are choice snippets. If BF3 can pull it all together for a good campaign AND multiplayer experience, I'll gladly move on from CoD. However, the so called CoD killers have been plenty and none have really lived up to the hype.
BF3 seems like a very worthy challenger, so let's wait and see how this plays out. At the end of the day, this is great for gamers as it creates competition and forces developers to up the ante and produce better quality games.