Pros:

-Has a very "legit" feel to the campaign.
-Feels like an official campaign designed by VALVe.
-Challenging on certain difficulties, but that's what makes it fun!

Cons:

-The level before the rescue level, when the train leaves without someone, the whole team fails. There needs to be something that tells you to get everyone to hop on.

Conclusion:

Very nice campaign. Would recommend it to anything who wants to play a good quality campaign