I'm not sure how much it will sell, lots of great FPS games coming out this year like Haze, UT3 and CoD. But this game has already passed 2mil last i heard so its just a matter of time before each game is sold. Its a great game, just about finished my third time through the story, along with 50+ hours online, its lots of fun. And i'm not a big fan of playing online FPS games.
I just like to piss people off online with my mic, and stalk my team mates and bother them, i'm the one blowing up cars as my team mates run by :P