Is Killzone’s Reputation Deserved?

Killzone has a reputation for being the PS3’s flagship franchise. To pick a representative quote from IGN’s recent preview of Killzone 2:

"Since that video at 2005’s E3, Guerilla’s Killzone 2 has earned itself – for better and for worse – a reputation as a flagship title for Sony’s PlayStation 3 and the console’s ability to usher in a new generation of fully immersive digital entertainment."

But why is this considered such a flagship franchise? Does it have a reputable developer, were early Killzone titles particularly loved, or does this title hint at to do something really new and exciting? No. None of the above.