This is, no doubt, the best L4D2 campaign I've ever played. It's like a bunch of different campaigns mixed into one long and great adventure. Well detailed, well executed, and overall fantastic.
By the way, I'm posting this review right after my first walkthrough of this map, and I was on a mod downloading streak, so I didn't check the screenshots, nor the description before I played it. This was a blind walkthrough full of surprises.
Now, what can I say about the chapters:

1. Woods: "I can't see sh*t. I hear a witch. Oh, there's two of 'em. Well sh-."

Bots are very lucky to see enemies in complete darkness, they took care of the zombies, while I was making quick runs from one light to another. It wasn't a usual L4D experience, but that's what made it interesting.

2. Underground: "This is quite normal."

I can't say a lot about this one, as to me, personally, this chapter wasn't really noteworthy. Not bad, but nothing special. (Except for that bloody Tank. It took me a good twenty seconds to grow enough balls to jump down, because I could hear the f*cking thing, and I knew that I'm going to have one hell of a fight down there).

3. Laboratoty: "At least some light, now I can shoot properly."

This chapter was not that far from regular L4D maps, though there were some very interesting places, like the vents full of intestines. That was unusual.
And the ending of this chapter felt like the 'final escape', because the run to the elevator was very intense.

4. Prison: "I knew that this elevator is not going to get us to the surface. And we are going back down the ladder... Finally, now I need to find another way to the sur- Sweet mother of Alessa, what the actual f... I'm in Silent Hill..."

This chapter was the best thing to ever happen to me in L4D. It was absolutely amazing, and I felt very uncomfortable while playing through it, which is great. Of course, zombies are not nearly as disturbing as monsters from Silent Hill, but it's not something that can be changed.
I kind of want to try this chapter with the Lone Wolf mutation, but I also kind of don't. (If you don't know - the Lone Wolf mutation disables special infected spawns as well as the other three survivors.)

5. Church: "Finally, I'm out of that place. After that - I can't be surprised by anything."

And this is why this chapter felt somewhat... Underwhelming. After going back to Silent Hill after so many years - running through the crypts didn't affect me at all. It was interesting, but not nearly as great as the previous chapter.

Overall: Ten out of ten with a cherry on top.
Hell, I would've given it a ten out of ten just for the fourth chapter. I still can't get a hold of myself, it was absolutely amazing.

P.S. I may be slightly biased towards anything that is Silent Hill, but I just can't help myself.