# Next-generation co-op action gaming from the makers of Half-Life, Portal, Team Fortress and Counter-Strike.
# AI Director 2.0: Advanced technology dubbed "The AI Director" drove L4D's unique gameplay - customising enemy population, effects, and music, based upon the players' performance. Left 4 Dead 2 features "The AI Director 2.0" which expands the Director's ability to customise level layout, world objects, weather, and lighting to reflect different times of day.
# New melee weapons - axe, chainsaw, frying pan, baseball bat - allow you to get up close with the zombies.
# Four different Survivors. New story. New dialogue.
# More game. On day one, Left 4 Dead 2 features more co-operative campaigns, more campaigns and maps for the Versus game modes than Left 4 Dead, plus support for Survival Mode out of the box.
# Stats, rankings, and awards system drives collaborative play.
This is cheaper than the offer currently available through the Steam holiday sale. All you do is use the CD Key present to register the game through Steam and you can then use Steam to download the game in the future if required so there is no difference between this retail version and digital download.