Jesus, I love this game SO much! I didn't think it was possible to improve on perfection this much.
It's much more colorful, with more varied environments. There's SO much going on around you that you really do get the feeling that you're part of something bigger (hundreds of enemies at times, Brumaks and Seeders popping up out of nowhere, large squads of allied soldiers helping you out, the list goes on!)
They fixed all of the glithces from the first game--no host advantage, shotgun DDR, no more accidentally slamming into cover while you're running, it's AWESOME.
And don't even get me started on Horde--I've played that alone for at least 10 hours already