Pros:

Different, enjoyed it a lot.
TRAINS.
The crecendos are pretty different and really fun.
TRAINS.
The ULTIMATE co-op map, as well great for versus.
LOOK TRAIN.

Cons:

Not enough trains.

Conclusion:

Classic. I will play this very often :)

Pros:

Very new, exiting, something different everywhere you turn.
Not many bot problems.
Long enough but not too long.
Dialouge that fits it pefectly.
Hilarious wall graffiti.
I think the gaunlet works fine
Theres like 3 finales.
Epic piano.
The lake is a lie.

Cons:

Bot problems: The gauntlet in the manor, and  getting on the rescue vehicle.
I did everything you said in the trailer thing at the begining, and my game crashed. 
Nothing else.

Conclusion:

Overall one of the best custom campagns I've ever played, I LOVED portal prelude so why not love this?