Pros:

-Good atmosphere
-Large map, lots of space
-It does have a lot of places to go, all of which are reminiscent of Silent Hill

Cons:

-Not really optimized for Left 4 Dead 2. As you said, you ported RP_Silent Hill which is more designed for Gmod, HL2, and CSS. 
-I couldn't seem to find any survival spots that suited me. I may be just nitpicking, but I'd like it if you could change it a bit so some of the survival spots can be held better. You know, until 2 tanks come about 3 minutes in and screw your team over.  

Conclusion:

Overall, the map is good as far as atmosphere, appearance, and the size is huge, a lot to explore and a lot of places to hold out. It really does need some work to be better optimized for Left 4 Dead 2 however. In that respect I'd say this map is a little ways away from complete, but it can be done, and I hope that it will be. I'll keep an eye on this map.