Make sure you have a lot of time to kill before starting this campaign, because you're gonna spend a good chunk of your time in these maps.
Loved the custom models you threw into this. Even though the new weapons, survivors, and enemies are a mixed bag to some people, I absolutely loved the effort in these new mods. Seeing a Siam bearing down on us for the first time through a foggy street was enough for me to high tail it in the opposite direction. Add that with the creepy music provided, and it's one heck of a foreboding experience.The music and sounds itself add a lot in building up the atmosphere, and along with some wonderful mapping, I truly felt I was transported to that quiet town. Overall, you've nailed it on the head with recreating the SH experience in left 4 Dead 2.
Of course, it does have its downsides. The hard-to-navigate lighting can get frustrating most of the times, which IS part of the SH experience, but is still an unavoidable flaw. The weird, high contrast lighting is a thing I need to bring up as well. is that intentional? Because if so, then it does add to the signature look of the SH games, but it is rather strange to look at, I must admit.
There is a LOT of wandering and backtracking in these maps, which is a staple of old school survival horror, lest folks forget. You've incorporated that wonderfully in this campaign, though I understand that it might not fit well with the fast paced level design most L4D2 players are accustomed to. As everyone says, be prepared to burn through hours playing through this campaign.
And the ending--ah, a hotly discussed issue among the commenters. Without spoiling much, it was still a very plausible and reasonable ending to attain. I must admit, by the second to last map, i was afraid there would be a sudden genre shift, and this would suddenly become Questionable Ethics or something, but it wraps it up nicely in the end.
To those unsatisfied/stumped with the ending: Remember that being in Silent Hill does not guarantee you a happy ending, and this custom campaign reflects on that bleak truth. What we've got would be something akin to the Jacob's Ladder conclusion, and that fits in perfectly with all the elements of this mod. (Look up Jacob's Ladder if you don't know it; it's one of the inspirations for the Silent Hill franchise)
Overall, the mod is a very well constructed experience delivered phenomenally well through a medium that is a stark contrast to everything the Silent Hill games hold as its identity. And the fact that you have managed to accomplish such a feat is very impressive. Kudos to you, man.
TL;DR - Don't expect a quick fun experience, or you'll be disappointed. Sink your teeth into the marrow, and let yourself get immersed in Silent Hill.
Hot damn, that was fun.