Pros:

Fairly solid
Not boring
Has potential

Cons:

Some low res issues, specifically on the far side of the broken bridge where you first enter the sewer tunnels.
Glitch on the map with the fire, for some reason it started my friend and the bots in the finishing safe room instead of the beginning one, they all died on the previous level maybe that's why?

Conclusion:

Like has been said before, a little optimization and some little fixes and I think you got a good campaign. Oh, one other thing the map with the fire in the building was really short, maybe incorporate that into the previous or following map and make it a 4 map campaign.  The final map had issues too with the sky just being black and flickering and gray blobs.  Also the finale was real easy.  Maybe do something different with the ladder to the copter, change it to be a "fuel up the chopper" type finale like the finale of Dead Air.  Overall I'd say it's a solid C~C+.