Left 4 Dead is a fun, but compromised experience. It's by no means bad, but it definitely feels undercooked and lacking in content, especially by modern standards.

Valve seemingly agree with this as they would almost immediately begin working on the sequel, in my opinion completely replaces the need to ever play L4D again.

In hindsight it definitely felt like I bought into a beta test for Left 4 Dead 2, but at the time I still had a lot of fun with it.