Pros:

Good length, never overstayed its welcome
Interesting and fun new gameplay mechanics 
Good level design
Loved the fog effects
Liked the ending/trailer theme
The intro was pretty cool

Cons:

Too many zombies (especially on the second chapter, the hordes seemed near endless)
The last chapter was a bit disappointing, though it was still enjoyable
The AI was very iffy when it comes to the raft at the end, they fell off a lot

Conclusion:

A pretty damn enjoyable campaign that in my opinion, was enjoyable as a campaign made by Valve themselves. It just had a few issues, that while some can be overlooked, some cannot easily. Though, it is still an enjoyable campaign.