I'm actually hoping the SP campaign could be worth playing. The atmosphere looks cool, but I just have no idea how they're going to fill an entire FPS campaign without it all getting boring and repetitive.
I was watching an interview and Randy mentioned one thing he's really proud of is the AI of the aliens. So if that's true, hopefully constantly fighting off aliens is always unique and fun. He also said they also took some elements from left 4 dead where the aliens will randomly spawn so it will always be a different experience in SP.
There's also the meta feature to the game that you can build up your characters identity and abilities in the SP that carry over to the MP. Randy mentioned its where you'll want to play your favorite chapters over and over again.
I'm not saying the SP won't get boring/repetitive, but there's at least some elements to it that will help possibly avoid that.