Akia said:
The single player not being the focus effects more than just the campaign's overall length. But the scope, scale and overall density of the entire single player. I don't think that the consequences are that simple (i.e: just subtract 3 hours because of multiplayer). Its more like we didn't allocate enough resources to make these set pieces and to develop systems that overall would make the single player better. To use your example: because of multiplayer those base 8-12 hours in your "with-multiplayer" scenario are not going to be the same as the base 8-12 hours in your "without-multiplayer" scenario.
Because of multiplayer, they're going to be focusing on under-the-hood systems that can be carried over into the co-op and multiplayer modes. Rather than developing everything that's necessary to exclusively make the single player top notch.
Why would it affect the 'scope, scale, and overall density'? Let's face it, the Uncharted formula is not rocket science -- they've established the core mechanics and basic gameplay features. All that they're really doing for the sequel is refining those mechanics and then developing a series of set pieces and kill boxes while fleshing out story segments in between. The bulk of the production, at this point, would have to be art-related (developing new levels, set pieces, etc), but it should have no affect on the density or scale of those individual levels.
Secondly, a multiplayer mode will likely rip out art assets already created for the single player and tweaked slightly. It will take some development resources to implement, for sure, but more on the networking side of things and not the art side of things.
And perhaps in the process of playtesting the multiplayer, this will make the single player experience better. Perhaps they find some aspect of the multiplayer is incredibly fun and engaging, and they want to add a similar experience in the single player.
I don't think Naughty Dog can really screw up the single player aspect of the game unless the cutscenes and story are not up to par with the original (unlikely). I loved the original because of the gunplay and the story -- how genuine the characters were. The great atmosphere that the art and music aided in creating this wonderful adventure tale. I don't think they can really screw that up with the sequel by adding a multiplayer component.
BTW, I really hope that Uncharted 2 has some Uncharted 1 levels in there for the maps. I'd love to play some multiplayer levels in a lush jungle and fortress environment (I really hope Uncharted 2 has similar jungle settings for the single player as well).