Pros:

-Awesome Locations
-Cool infected models
-Music and sounds from the SH2/SH3 are included
-Intense opening level
-Heavy Challenge
-Fun online and offline
-Unique areas
-Fun Exploration
-Characters are in sync with world. (When they pass by a sound or hear a noise, they will say "What was that?")
-Funny cameo of L4D1 survivors in woodside apartments.

Cons:

-First area (Nowhere level), has nav issues.
-Dark Forest is too dark (Could not find exit)
-Crash in 4th area on way to apartments

Conclusion:

One of the best on this site in my opinion. Very good. It would be worthy of a 10/10 if you can fix the issues i listed in cons.

(PS. Please include central square mall from SH3! I love that place!)

Added to watch list.