Today Valve are adding a new community created campaign onto our official servers called "Warcelona".
You can download it from here and copy that file in your Steam\steamapps\common\left 4 dead 2\left4dead2\addons directory. You can also double click it and it should copy it there – but if it doesn’t, you can just move it there and then start your game. Having it on Steam's servers means you can start games on an “Official Server” for a better experience.
The Left 4 Dead 2 Workshop has been in a test beta and will be expanded into an invite only private beta this week. Using the workshop will allow you to simply click a subscribe button and you have them map! It’s that simple.
Steam are also launching a new event titled: "Meet the Creators". For the inaugural session, they will be having a chat session this Saturday at Noon PST with the team behind Warcelona and some of the Valve devs. It will be a mix of playing and chatting so stop by the Official Left 4 Dead 2 Game Group and join the chat. If you can’t make it then, download the campaign and check it out.