Pros:

Custom sounds
New mechanics
Interesting story
Stargate
Animations
Textures and models
Variety of locations

Cons:

Minor bugs
Can be hard for beginners

Conclusion:

I enjoyed this campaign very much. I haven't watched the Stargate series, but it showed me what this is about. When you will see the Stargate as a gate in this campaign you will be shocked how awesome it looks. Some other good things are the new mechanics like oxygen masks which you have to fill with (of course) oxygen or shooting the fire extinguisher to put down the fire next to it. The campaign has got some new audio when something happens or when someone talks to you. There are some good graphics too - some new textures and models and animations - perfect example of all three is Stargate. I recommend this campaign to everyone, but if you are new to Left 4 Dead play it on lower difficulty.