Seriously, Killzone 1 is completely irrelevant when comparing to Killzone 2. Killzone 2 is entirely different, and its going to sell for lots of other reasons.
IMO this and MGS4 are the only games I can look at that really justify paying $399 for a console. If you showed me these games back in 2005 I wouldn't believe it was possible. The same can't be said about any other games, except maybe Gears 1/2, Resistance 2, and LBP.
The graphics ALONE will justify purchasing this game for lots of people, but the gameplay is looking extremely well on top of that. In Killzone 2, I think Sony has found its answer to the Halo franchise. If Gears 2 can 7-8million lifetime, I don't see why Killzone 2 won't be able to pull at least 4,000,000 since the install base of both consoles will be almost identical by then.











