Yesterday, Valve announced a new $25 million ad campaign for the upcoming game “Left 4 Dead 2.” Valve states that the pre-orders for L4D2 have been flying off the proverbial shelves, and is predicted to be the fastest selling product in Valve’s history.

Valve intends to run advertisements during Monday Night football and UFC broadcasts, put ads on billboards, and on lifestyle and technology websites (Hey!). They’ll be showing television broadcasts internationally as well, with tons of print and online advertisements.

Left 4 Dead 2 is being billed as a game that far surpasses its predecessor, with the AI Director changing weather, world objects, pathways, and the zombies to suit each survivor team. There are also new zombies, weapons and more campaigns than the original L4D.

With all of those things going for it, and rampant pre-orders, we’re wondering why Valve is spending so much money to advertise the game. The original L4D did very well on only a 10 million dollar advertising campaign, and we didn’t find another game that had such high advertising costs.

One likely reason Valve is dropping the big bucks is because of the angry backlash from players of the original L4D about the release of a sequel so quickly. (L4D came out on November 18th, 2008). While the new game does appear to offer a lot of new content, players argue that that same content could be released in updates for the original L4D. They also contest that the amount of bugs that have not been corrected in the original game are unforgivable. It’s probably a fair assessment to assume that many of these angered players may not be buying the game right away, so Valve could be attempting to compensate for that loss.

It’s also possible that Valve is simply trying to capitalize on the current popularity of zombies, and has the money to spend. The release of the well received movie “Zombieland” has put zombies back on the public radar, and the success of zombie games like the original L4D or “Plants Vs. Zombies” from PopCap games shows how pervasive their appeal is.

Left 4 Dead 2 launches on November 17th. You’re likely to see a good deal about it before then, so be on the watch for zombies invading your billboards, websites, and football games. Forward pass to the boomer, anyone?