Play the if you have beaten the single-player twice and own a second copy for testing. Avoid if you are not comfortable editing user.cfg files or troubleshooting DirectX errors.
There is an active community project for the tactical shooter Operation: Harsh Doorstop aimed at creating a multiplayer experience. : Large-scale PvPvE or co-op missions. metro 2033 coop mod
Interested in trying out the mod? Here's a quick rundown of what you need to do: Play the if you have beaten the single-player