Go alone, or invite a friend for 2 player co-op against the zombie apocalypse in all 4 of the original game campaigns. 2 difficulties and all 4 of the survivors make a glorious 8-bit appearance, complete with first and second tier weapons scattered along your path to escape. So, grab your controller of choice and kick back with an award-winning retro take on the end of the world with Pixel Force: Left 4 Dead.
Here's some gameplay footage:
You can download it.