Most of Killzone 2's hype that makes it infamous was back when the game was first announced with its CGI trailer at E3 in 2005. Over the years though the hype began to fade quick as year after year went by with no sign of release. Just a few months before it did both Resistance 2 and Call of Duty: World at War were predicted to be much bigger FPS releases for the PS3. Then as December 08 rolled on and we finally got some real time trailers and gameplay videos for Killzone 2 the hype train hit again up until release.
It's worth noting that even with all the hype that Killzone 2 received, there was far more anti-hype for it mostly due to its prequel's status as one of the most overhyped games of the decade alongside Daikatana and Fable. There were just as many detractors insisting that the game was going to be subpar due to the prequel's legacy of overhype. It's for this reason that Killzone 2 is considered to have delivered well beyond the expectations of many despite the amount of hype it had.