We can become pretty calloused toward user created mods, but when someone goes to the effort of recreating Resident Evil 2's entire scenario in Valve's Left 4 Dead, our cold hearts melt.
Such is the case with Bioh4zard 2, a work-in-progress user created campaign that recreates the locations — but not necessarily the exact events — from Resident Evil 2 in a Left 4 Dead episode.
The creators, known as Zac-UK, jonmag and petbird, are going full bore, rebuilding Raccoon City's police department, sewers and Umbrella Corp. HQ in the Source SDK. Obviously, there won't be Lickers skulking around in the campaign, but Left 4 Dead's Smokers will be an acceptable substitute.
As already covered, this is a work in progress, but there are loads of screen shots for you to soak up. Perhaps you'll recognize a location or two.
Bioh4zard 2 - Full Campaign - Work in Progress [L4Dmods.com - thanks, Sean!]