Killzone, the original, had the unfortunate circumstance of being a high profile FPS being published by Sony for the PS2. AT the time Halo was all the rage, and the media emmediately said that Killzne was going to be Sony's "Halo killer'. Now the game, on merits other than simply being some supposed Halo killer, was getting a fair bit of positive first impression attention. THe Visual design to this day is still probably some of the best ever for that generation, so you ca imagine how a real buzz was created with screenshots ad previews. Now the only problem was that Guerilla Games was a brand new studio, and were very ambitious with Killzone, in terms of pushing PS2 hardware. In the end Killzone simply pushed the PS2 too hard, and the game was plagued with technical issues like framerate, but also suffered a little bit from the team simply being new, and there being some issues with level design etc. So Killzone, despite selling well, sort of became the lauging stock of the fanboy world. Being that it was billed as aHalo killer, and failled to live up to that, and in actual fact was far from a perfect title (despite having stellar visuals and atmosphere, for the mot part).
Anyway, Guerilla Games went on to make Killzone Liberation for the PSP, which turned out to be great title. It was made as a top down TPS set in the Killzone world. Guerilla was bought up by Sony, and development on Killzone 2 started.
Now Killzone, you have to understand, was percieved by a lot of its fans, as a near miss, and a lot of people were excited to see them really let loose ona console that wasn't as restrained as the PS2.
Though Sony is Guerillas greatest ally, and foe, in a way. Becase shortly after the PS3 was announced, they had Guerilla Games produce a CGI target render of what they hoped to achieve with Killzone 2. Granted that target render was anight and day difference between it and anything else we had seen to date.
So anyway, Killzone 2 is finally revealed, it doesn't look as good as the target render, but it looks pretty incredible on its own merits. It's probably the most advanced console game to date and it's doing some really absurdly impressive thing, technically speaking. There are absurdly talented people working in Guerilla games. But the concern people still have, if will they nail the gameplay, somethin they came so close, but so far, from doing in the original.
Killzone is really paul verhoven esque, it's a sci fi future setting, but it's very gritty, with the primarilly weapons of choice still being conventional slug based weapons, etc. Take a look for yourself, see what you think.