As a shooter, it's overall fuck awesome, has some of the best skirmishes around, with weapons that feel great and enemies that offer up a real fight for their turf. And obviously the atmosphere helps a lot there. As a complete modern game, however, including things like writing and pacing, it's merely good (but then the medium isn't exactly flourishing with brilliant writing and character development). It's as if the company has matured to become one of the absolute top studios around when it comes to raw combat, but hasn't quite grasped the whole thing with storytelling, and the importance of likable characters. Which is honestly a bit odd, as I don't remember having much of a problem with any of the characters in Killzone, other than Rico. I even liked Luger, which I can't say about any of the characters in this game. The helghast have a hell of a lot more personality.
I think that, much like Halo 2 and 3, I'm going to be enjoying future playthroughs more, on account of being able to focus squarely on the combat without feeling like I might miss out on story by skipping the cutscenes. It's not even that the story is bad, it just feels poorly presented.
About game length, I don't understand how anyone can get through this game that fast. I'm at 8 hours, and I still have some ways to go.