This game was on my radar long ago, but had since forgotten it, discarded the idea of playing it. Now that I watch this, I think I might actually play it, if only because FPS campaigns can blazed through in a couple of days and I've yet to play one where we shoot up koreans, save Crysis -- amusingly, Crytek is making the sequel to this. I just realized though... this is yet another game depicting war on american soil. I've been playing Crysis 2, which has just that. Modern Warfare 2 introduced it in that series, 3 continues and Battlefield Bad Company 2 also had it which, I think, BF3 also continues. Not sure, I forget. Then there's the RTS, World in Conflict (not to mention Red Alert, which doesn't count as its a classic series that has a plot long predating this recent trend).
On a final, I find it part sad, part amusing, that some of you consider this a realistic premise. You know too little of geopolitics if you do. If it were China, then maybe. Not entirely, but definitely more so. If anything, considering how oddly they (NATO & UN) have allowed that country and its regime to grotesquely expand borders (Tibet) and its economic and military might (nigh slave labor by hundreds of millions).
Best Korea, though? Pff. It's really a miniature version of the former Soviet Union. That's the best way to describe it in a sentence, presuming you know enough about the latter. Honestly, I'm not sure they could beat their southern neighbors even in a 1 vs 1 showdown, much less annex them, Japan, others, and invade North America. Laughable.