Battlefield 3's Caspian Border? That's 2.21sqkm. Just one of Planetside 2's continents? 64sqkm. I can tell you right now that it's going to take a while to drive that Advanced Nanite Transport from your base to the warp gate and back again. Assuming you don't get exploded, of course.
Click the image above for a full-size, non-cropped version.
If you're wondering where the Battlefield 3 map is, it's in the bottom right-hand corner.
While they're both online and highlight huge multiplayer battles as a draw card, Planetside 2 and Battlefield 3 are very different games. The point of the image (at least, from my perspective) isn't to start an argument over which one is better, but simply to illustrate the scale that fights in Planetside 2's will occur on.
Delving into the role-playing genre, Skyrim's land mass is a meaty 41sqkm, which is getting close to being on par with Sony Online's upcoming MMO shooter. Well, except for the fact Planetside 2 will have more than one of these continents (the original game had 13), bolstering its credentials considerably. Like Skyrim, they'll be hand-crafted. Unlike Skyrim, you'll be sharing it with up to 2000 other players.
But it's not a competition. Having loads of land does not figure well into quality equations -- just look at Bethesda's own Daggerfall...