Left 4 Dead 2: The Last Stand, the community-made update to Valve's multiplayer zombie shooter that's been adopted as official, is now live, and to celebrate the big moment Valve has made the game free to play for the weekend.

The Last Stand features a new campaign based on the original survival map, but this time around you can actually escape to safety—if you can blast your way through hordes of the infected. There are also 26 new Survival mode maps, four new Scavenge Mode arenas, a pair of new melee weapons—the shovel and the pitchfork, and for my money the shovel is the way to go because the pitchfork is going to get stuck on something the first time you use it—and 30 new achievements.

Less visible improvements include new animations, the restoration of unused dialog, the addition of common infected models from the original Left 4 Dead (with gore!), new Rocketdude and Tank Run mutations, UI improvements, and "a ton of bug and exploit fixes." If you'd like to dive into the details, the full patch notes are available here.

To ensure everyone has a chance to see what the big update is all about, Left 4 Dead 2 is free to play on Steam until September 27, and if you like it and want to carry on with the zombie-blasting shenanigans, it's also on sale for 80 percent off—that's just $2—until September 28.