Buy it.
The visuals in Killzone 2 have almost a dirty feeling to them. You can stare in to the screen and find the jaggies if you want to and say hey the graphics are not that good or you can look at the whole picture. Dynamic lighting, combined with character models that offer realistic facial impressions and a body language that acts true to life.
The Multiplayer is unlike anything ever experienced. The fact that matches are strung together and they give you new objectives the minute your done one is totally new. Now some might say the experience system has been done and yes it has. Call of Duty 4 and Call of Duty WAW do this very well, but what they dont do is give you character classes with and experience system on huge multiplayer maps that make you feel as if they laid out every object on the screen with such careful planing and placement.
Killzone 2 is I think is a new stage in fps games. It ups the level on almost everything that it does. Games today need to stand out and dare to be great. Killzone 2 does this in almost everyway and definetly goes on my handful of great games list.