What it comes down to is that if Guerrillla gets this right, meaning the quality of the gameplay matches the presentation, it will be one hell of an event, a milestone even. Multiplayer seems to focus on all the right things, and it looks amazing. At this point, though, I'm not ready to assume that they will nail it, although I'd say it's probably likely that at least the multiplayer will be awesome.
In regards to Resistance, on the other hand, it's all but guaranteed that it will be at the very least good and polished. And the multiplayer options, from the 8-player online campaign mode to the 60-player online competitive mode, are well above the norm. Looking at the games without consideration for the featuresets and sheer numbers, it feels like KZ2 is the riskier, but it could mean a higher reward. We'll see.
Resistance 2 does seem more superficially barren and "engineered," though. I suspect that its sci-fi settings will look remarkable, however. But Killzone 2 is quite obviously, on a visual level, the more creative and inspired of the two.