I've only played the MP beta so someone else would have to answer about SP (there is allegedly a big difference), but MP felt far more detailed and technically more "impressive", but me personally, I preferred the cleaner, less detailed style of Resistance 1. MP also felt overly bloomy, to the point of appearing blurred and smeared. Not a good look, IMO. But I think objectively speaking, everything leans heavily in favor of Resistance 2.
Now Killzone, on the other hand, is hot. I thought Ratchet looked great in its way, and Uncharted was impressive in its way, but this is truly a cut above. It presents a cohesive, very strong artistic vision, powered by what's now obviously very solid and stable technology. The last bit is the most surprising of all, to me.