Pros:

First four maps are nicely designed and just about right challenge wise
Avoids the unbelievably boring going round in a circle map design so many others have decided upon

Cons:

No ammo in safe rooms, and there's not always one variety of rifle, sniper and shotgun to make up for it
No tier 1 weapons at the start of the first map (always a bad sign, the exception is The Passing, where they're in the first room after the intro)
All begins to go downhill on map 5 - goes from being challenging on expert to downright ridiculous - an event and then a gauntlet at the end with no kits or even a reasonable amount of pills/adrenaline makes it all but impossible
Finale is even worse - SI continuously spawn before you activate it, there is absolutely nowhere even remotely safe, and then the classic - 2 tanks on the second wave - just how do you expect people to be able to evade 2 tanks at the same time when there's water slowing you down everywhere?  Oh, and there's uncommon infected during the finale as well, just to put the icing on the cake

Conclusion:

The first four maps are great, slightly derivative in places but perfectly fine considering the game's limitations.  After that, the difficulty level just goes off the scale.  And it's not just on expert - the finale is difficult enough on normal when you're playing on your own.  Ruins what would be one of the best custom campaigns, alongside Suicide Blitz and Death Aboard.

Pros:

-very fun
-low gravity is amazing

Cons:

-TO MANY ZOMBIES SPAWN AT ONCE
-only good with friends 3 or 4 people
-To get to the rocket area takes forever

Conclusion:

i find it very fun but i never play this alone or with only 2 people