I just finished the story mode of MW2; of course I still only received a 50% completion due to not getting all the items etc… I may actually run through it again just for the fun of it and to get that 100% damn it!
I love the immersion of the game play, getting the refresh course (though not really needed for most of us who played the previous games) but it is helpful still. Bouncing back and forth between some new and some old characters all over the world was very fun and kept my interest throughout the game.
Spoilers below