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.

Pros:

Has good graphics.
Chainsaw appear when you need them for hordes.

Cons:

Consistent hordes for little to no reason.

Bots still lag behind.

Common infected during the first tank in the finale level is just cheap, it's best to have them stop spawning all together during a boss fight.

Speaking of cheap, the last tank spawned where you where supposed to go and I had no gun to fight him with and wasn't going to bother saving bots.

Poor placement of tier 2 weapons, and bots pick the first tier 2 they can find if they can't use their preferred weapons. It would be better if they appeared in the second map as suggested by reviews before mine.

Conclusion:

This is one of the most overrated campaigns that I've played. There is nothing but consistent hordes for players to deal with, which is why I knocked forty points off as it's just cheap and not enjoyable unless you think having ten common infected beating the crap out of you ninety percent of the time is fun. Warcelona right now is too difficult and frustrating for the average player.

Pros:

It looks good.
An M2 that isn't completely useless at the finale.

Cons:

No health kits at the start.
Bots are stupid, they lag behind a lot.
Bots don't get into the chopper and you have to shoot them so you can win.
Most areas are cramped and small, and all maps past the third poor hints to to reach the safe room.
Lack of Melee weapons and ammo pick ups.
M60 only appears at the finale. 
Feels like it created for L4D and compiled for L4D2 at the last minute. Most Left 4 Dead 2 features look like afterthoughts.
Tank got stuck in the sewer, making for an easy kill from above.

Conclusion:

What could have been a good campaign turned out to be pretty average due to bugs and poor path finding for players.