in the solo campaign. Online, you either make it through an entire map or you don't, which can be a little frustrating on some of the longer maps.3.) You don't get all of the "story" elements, or many of the "training" elements that you get in the regular solo campaign. The story isn't necessarily a huge problem since the map still tells you where you're headed. (And half the time I forget to listen on solo anyway.) But you really do miss some important training stuff (especially if you don't get too heavy into reading the manual...ahem.) So it really pays to play through at least the first mission solo, just to get all of the details on how to use your sound suppressor, switch grenades/weapons, use the snake cam, etc. You could pick all of this up by reading the manual, but...who does that?Honestly, this was the most fun I've had playing co-op. I enjoyed it more than Gears of War. Tactical, strategic, high-speed, and challenging (but not impossible.) Highly recommended.