A steroid PSA in the making.
You play as Sev. A member of an elite delta force like unit that gets thrown into against all odds situations and you are somehow supposed to win them all. And you do. You breach the outer defenses of the Helghast capital, to a speeding cargo train that is one of the best sections of gameplay I've ever had. One thing that never happens is that the game never seems to want to slow down. The gas pedal is to the floor the whole time and it's a wild ride. A million things are constantly happening on the screen and there is never a skipped frame or freeze. Unlike what my computer just did...
The Helghast are extremely capable opponents. They flank, hook, bait, throw grenades when you aren't looking, and have great aim at higher difficulties. Their are also different styles of armor for the different classes they have which is a nice touch. The weapons of this game feel tight and and loud.
One thing I didn't like to much about the game is the lack of depth with it's cast. They shoot at enemies, then yell obscenities at enemies, and then continue to shoot at the Helghast until they die. It get's a bit annoying after a while. And another thing is with so much action going on at one time there really isn't a 'holy crap' factor. How many buildings were blown up in this game, I have no idea.
The multiplayer is weak however. They servers might have a couple thousand people on them and they don't work half the time. So unless you want to get the 100% on the trophies list just skip this part all together because it's incredibly frustrating.
On the whole Killzone 2 is a fan-freakin-tastic game. Visually stunning, ultra-fast pace, and wanting to find out how this chapter ends is wonderful. It takes the original and shoots it full of roids. Which is probably why it's so angry all the time.