mrstickball on 22 June 2007
kn, I want to say there are around 13 missions on the adventure and war story sets. This doesn't include the extra free missions you can download (I think there are 3?).
Overall, OKX takes quite a bit of time to finish everything - I'd say 10~15hrs on your first runthrough not caring about gold medals.
Back from the dead, I'm afraid.
