Magnum,
And let's not forget that mission where you have to make your way across the bridge and fight your way through waves of bad guys and also take down a chopper.
None of the co-op missions that Magnum and I played were part of the campaign. It was all new stuff and it was all fun. The stealth mission, in the snow, was tense. You could opt to kill the bad guys but you had to do it quietly so as to not alert others of your presence. If they spotted you, you didn't live long. You'd get overwhelmed in hurry.
The C130 mission might be my favorite but it was the only mission we were unable to complete. Pretty difficult on "Hardened" difficulty, but it was a BLAST to play and watch those bodies go flying. It was a hoot to shoot down the choppers as they were delivering more troops and watch the helicopters blow up and the soldiers inside get thrown out. Great stuff.
The campaign in this game is ridiculously short but they've made up for it with this co-op mode and the quality of the MP component. Still, I'd have preferred a few more hours of campaign play.
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"All religion, my friend, is simply evolved out of fraud, fear, greed, imagination, and poetry."
Edgar Allan Poe