The Writer of Killzone is brilliant, the Artist of Killzone is brilliant, the Director of Killzone is an idiot, we're stuck with Rico and other dumb asses just shooting Helghast soldiers because its edgy and appeals to short attention FPS gamers who say "HURRAH!" and have an unhealthy secret gay crush with John Cena.
This issue is the same for Warhammer games, the games are about generic space marines killing aliens, but the backstory is about nations and emperors and civilizations, want to kill your story? make it a shooter.
Halo also has a good backstory but that back story was written after the first game (after halo 2) so it was easier to implement.