You didn't think we'd let a weekend go by without a Left 4 Dead post, do you? We've totally been enjoying the zombie killing co-op here at Co-Optimus HQ. One of the coolest parts of the game, in my opinion, are the achievements. The best achievements add even more value to a game, and that's exactly what Left 4 Dead's do. Play through a campaign with pistols only? Tough, but fun. Set a tank or witch on fire with a molotov cocktail? Ooh, that gives me the chills. Valve has done come interesting stats work on the PC version of the game, detailing what percentage of players have earned each achievement. Here's a few highlights.