I've played every single CoD game, from the original PC game to all the console versions. My ultimate favourite was "United Offensive", closely followed by CoD4:MW and CoD2 (or WaW - can't decide!). Since CoD4:MW, the SP versions have been ultimately rather lightweight (WaW excepted) - I enjoyed MW2, but it just wasn't meaty enough in SP; Black Ops had a great SP story, but was again too short (& too easy on Veteran). MP kept me going for a while, but once you get fixated on K/D ratios in TDM, it's time to put it down and play Ratchet & Clank instead...
I've got the MW3 Hardened edition on pre-order, and no doubt Mrs Bones will become a MP widow for a couple of months, but to be honest, I'll be amazed if the SP campaign takes me more than a few hours to complete.