Killzone 2 doesn't have a shot at being a full-on "Halo 3 killer" because it won't be released until 2008. But, just because the games don't release at the same time doesn't mean we can't compare the two system sellers. After all, both are first-party first-person shooter sequels, and while Killzone 2 won't compete with Halo 3 in September, it may be able to steal some 360 fanboys when it launches a couple of months later.
From what Sony showcased at E3 2007, Killzone 2 could very well help tip the sales scale in PS3's favor. The stage demo featured graphics that were darker and moodier than the first Killzone game on the PS2 and anything we've seen from the Halo franchise. Its mostly black, brown and grey textures took on realistic lighting effects with all of the non-stop gunfire going back and forth between you and your monstrously-sized enemies. Their orange eyes were the only element that really stuck out against the darkness besides the constant spray of bullets. If you look back to the infamous 2005 demo, it features the same sort of frantic chaos as this for-sure, real-time demo.
Like the Halo series, you can carry two guns at a time, including an assault rifle, sniper rifle and rocket launcher according to the E3 demo. All three of these powerful weapons were shown taking out enemies using a built-on scope. Presumably, you'll be able to press a button to look through the green lens and zoom all around to place your shot. The effects are pretty gruesome, too. In addition to seeing enemies throw their weapons away and fall to the ground, they'll start to ooze with a lot of blood. Better hope none of this takes place in a church.
When you're the one taking the bullets, the screen begins to fade to black and white, which is becoming a little too common these days. The idea behind games that do this is that it reduces the need for HUD information like health bars and focuses you in on the high-def action. Killzone 2 follows the trend by taking away the HUD completely. We'll just have to wait to see how you count your remaining bullets since the demo didn't explicitly make that clear.