I used to make fun of Killzone, but ever since the third game (which I loved) I've been onboard. Mostly - and this may shock you coming from someone who runs a daily art feature - because of the design of the world.
Yeah, the Helghast are silly, but there are so many fantastic touches to the visual design of the Killzone world. Not only can it be surprisingly pretty, but there are a ton of dirty, practical little touches. The kind of attention to detail that can really bring a world to life. Take the guns, for example, which look like functioning guns, not an artist's space toy.