Mind Explaining Killzone Somone?

Kay, I’m a bit interested in Killzone 2, and my friend steve says when he gets his PS3 he will get it and let me play (he usually doesn’t do that, the “let me play” part)

My friend rented Killzone 1 once before, but he used a cheat to unlock all levels, so we didn’t even learn the story line, I heard it wasn’t that good, but could probably be built off of.

Can someone just explain the story a bit and what it’s about?

A group of marines were investigating a mysterious crash near the city of Roswell and found a radioactive, flying moose that could shoot laser beams.

http://www.gamespot.com/ps2/action/killzone/review.html?om_act=convert&om_clk=gssummary&tag=summary;review