Well, that was fast.
That's the reaction everyone (including me) has had. However, if you look at the release dates of the series (
http://en.wikipedia.org/wiki/Battlefield_(series) ), then you realize, perhaps with some disappointment, that this is right on time. Even discounting digital-only and free-to-play games, the gap between Battlefield: Bad Company 2 (3/2010) and Battlefield 3 (10/2011) was only 19 months. Assuming Battlefield 4 is another October 2013 release, it is a gap of 24 months.
Since 2002 when Battlefield 1942 came out, every year has had at least one new Battlefield experience being released. When you discount expansion packs and free-to-play entries, here is how the gaps look like:
BF1942 (9/2002) -> BF: Vietnam (3/2004)
18 months
BF:V -> BF2 (6/2005)
15 months
BF2 -> BF2142 (10/2006)
16 months
BF2142 -> BF: Bad Company (6/2008)
20 months
BF:BC1 -> BF: Bad Company 2 (3/2010)
21 months
I probably messed up my math somewhere/everywhere. To my surprise, the gap between BF3 and BF4 will be longest between major Battlefield game releases. You can make the argument that the spin offs don't count which is fair though I don't agree with it. From the perspective of that argument, this will be shortest time between "mainline" Battlefield games.
At first I was a bit angry at the news as I bit the Battlefield 3: Premium bullet (I do really enjoy the game and want it to be expanded), but after looking through the release history of Battlefield I calmed down. It is a bit surprising as hearsay talked of Battlefield: Bad Company 3 being the next game.