Maybe I'm just too old, but it felt like I was watching a Soap Opera in the campaign. While one story was picking up momentum, another story from either the past or present would cut-in and completely ruin the flow. I was actually getting aggreviated hearing the old war vet talk and talk in between missions. It's a FPS for f sake. Don't make it a mindless FPS, but if you're going to take the risk of making a story, make sure you tie it into the action.
I didn't really understand or how doing one mission before the other effected the story either. You were going to get the same dialogue and outcome no matter what you did, until the very end, at least.