Just started playing the first DLC episode yesterday. It's pretty fun, but extremely basic in terms of missions and all that -- definitely not up to the standards of the regular campaign.
It also seems there's no time limit, which is awesome if you want to go around the open world just for fun. It's less beneficial than it would be in the regular campaign, however, since there's not as much to do.
Yeah no time limit, but if you are one for collectibles or achievements, make sure you hack the Cameras, collect Dog Tags and find your team before moving onto the next area.
My major problem was that it is way too short, like $13.95 Australian for a maximum of 2 hours gameplay? Ridiculous!