Hmm, I guess I just don't get what N'Gai is trying to say, or wants to say but can't despite his impressive diction.
The thing is, "realism" isn't always beautiful, and to depict something meant to be realistic (in the case of GG's "Killzone" series, just 'war perfected', yes?) with blue skies or out-of-place colors cheapens or perhaps in some cases completely ruins the immersion of the game and, further, the intention of developers to show what they clearly want to show.
Consider, I guess, the film "Aliens" -- perhaps one of the most depressing films I've seen (Ebert shares a similar feeling, check out his review), and is almost physically draining in the same way that, perhaps, Silent Hill 2 is -- while sharing nothing in the way of content. I got a similar feeling with Killzone 2; it evokes an absolutely dreadful feeling, and realism simply seeps out of it. Is N'Gai trying to say that he doesn't like that absolutely spot-on rendering of a futile and depressing future war? If so, okay, but accept that it is an absolutely spot-on rendering, and that it's simply not to your liking. There are plenty of colorful games out there; certainly happier ones, that maintain some realism.
As for "beauty" -- well, Killzone 2 is a beautiful game, but only insofar as it nails the theme of war. I'm not alone in the world when I say terrible, terrible things can evoke a bizarre sense of beauty; a spider eating another spider, for example, is both disgusting but evokes a strange, intangible sense of order in nature which in and of itself is beautiful in a very primal sense. Killzone 2 is that kind of beautiful; it's ugly in every other sense, but in it's rendering of ugliness, it is no less than almost perfect -- for that, I can say, I do not understand N'Gai's point one bit.
But I like him. He's a cool cat.