Pros:

Big environments.
Reminds me of the Aperture Science facilities.
Loved working through the Test Subject cells to the surface.
Polished Levels.
Inmersive.

Cons:

The third level not as polished, but it's not that important when you're running constantly.
Too hard, we were playing on Realism Normal (2 People) and had to put it on Realism Easy 3/4 of the last level, thinking we wouldn't of made it otherwise.
Wish there were less fake doors.
Not really clear where to go.

Conclusion:

Fun campaign. I'd love to see more like this, just not as hard.