Tried the Killzone 2 demo over the Playastation Network. It’s a rather fun game which isn’t too challenging on the normal difficulty. Being a demo, it was woefully short and lacking in content but from what little I saw it looks like a pretty good game.
I’m not familiar with the story, but it seems to be a human invasion of some sort of planet from a different dimension. The baddies are called the Helgast, and I wouldn’t be suprised if this alien dimension is a paralell one as there is some remarkably familliar Helghast techology.
Their assault rifle looks like a FAMAS rifle with some shiny attachments, and they have gas bottles which look exactly like the ones you hook up to your barbeque. The gas bottles themselves are rather fun and useful. A single shot will produce a fuse like effect that spews out hot gas to the point the barrel explodes violently.
This can be used to create traps for eneimies, setting off stockpiles of these things. The escaping gas can also propell the barrel around, moving it in a particular direction or just spinning it on the spot.
The side-handgun has infinite ammo, making it rather broken and far too powerful. Grenades and a knife round out your arsenal, with the grenades producing light which handily illuminates where they have been making anticipating where it’s going to go much easier.