Pros:

*Maps one to three are actually pretty good with three receiving the most improvement in L4D2.

*Dark atmosphere that fits in with the Left 4 Dead survivors.

*Maps are more balanced for infected than the Left 4 Dead version.

Cons:

Now this is where points will get taken off so please fix them if you want a higher score.

*No Left 4 Dead 2 weapons, or they never spawned . Seriously heading towards a military base and no FN Scar or AKM in sight? - 10
*No Desert Eagles -5
*Very few melee weapons -10
Map four is a let down and the lowest point of the whole campaign, the cartoony looking crates really killed it for me . Some parts such as the mine also look really bad, Map three could also use some flickering lights instead of total darkness for a more creepier feel.
.-10
*Bots don't grab med kits at the finale, even while their injured and I'm not going to heal them while dealing with a horde or tank. -5

*Fortunato inflated the score due to fanboyism and ignored the fact that this campaign needs a lot of work on to make it better. -5

Conclusion:

This could have been a great campaign in Left 4 Dead 2 but the lack of features and repetitiveness kills it, on top of that melee weapons hardly spawn and it only uses weapons from the first game.
Also cording to some comments this campaign is quite buggy.

The transition between games should have been much smoother and more polished than this but players are obvious are  better off playing the Left 4 Dead version, but neither Dead Gateway release is much of a stand out campaign. So I would suggest players look for something better until these issues are fixed.