Like Battlefield. If you are buying it for single Player, you're doing it wrong!
I believe the SP is done well based on several reports of people playing and being drawn into the (short) story. BUT I believe the only reason SP is there is to give the game an identity in the marketplace. It calls attention to itself and the relocation to "home soil" (for many of us) is unique in that vein. In today's marketplace, even to sell the MP aspect, you need a hook, an identity. That's all this SP is.
do people buy 15 million copies of black Ops to play the SP as an operative? hell no. they buy it because all of their friends tell them how ADDICTING multiplayer is.
but black ops is an identity.
the game is built for MP.