Ok IMO about the CoD series:
CoD4: My fave, story was great, multi is fun
Mw2: Story was ok, multi had unbalenced weps, hard to follow story
Bo: Story was good and had a great twist, multi was improved from Mw2, i like the new gamemodes, zombies are always fun, lack of Veitnam :(
Mw3: Cue explosives montage!