The Left 4 Dead series has sold more than 12 million copies, Valve writer Chet Faliszek noted in an interview with VG24/7. Faliszek talked about the company's approach to promoting its games, saying Valve doesn't rely much on marketing because "when a game does really well at pre-release, they're going to know that you're not just talking a bunch of PR crap."

"We just let the game speak for itself because the internet has made this thing where you can't pull the wool over people's eyes any more. They're going to know you're hyping," he said. Either the zombie apocalypse creates some high-quality wool, or Left 4 Dead must be a pretty great series.

http://www.joystiq.com/2012/09/30/left-4-dead-series-sells-more-than-12-million/

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So I guess it's a somewhat fair 50/50 split between PC and 360.

In case of Valve games. Probably yes.

I could imagine that Portal 2 is also around that what the PS3 and 360 version did.

A multiplat HL³ would however still sell much more on PC I could imagine.

For Valve games that have been out for a long period, console versions won't even come close to matching the PC version in total sales. Part of the reason is that it's Valve, and all they really care about is the PC version, but also because of Steam sales. I think I paid like $5 for L4D2.

Valve is a strange animal.

Never been a fan of the L4D series, just found it lacked any real depth and lasting entertainment value. Zombies on COD was more entertaining and that was just a side game for that series.

I want more Half: Life!

Valve hates the number 3, it will probably be called Left 4 Dead 2: Episode 1 :P

Regarding Left 4 Dead 3
http://www.xbox360achievements.org/news/news-12977-Valve-Discussing-Left-4-Dead-3-Ideas--Including-Player-Controlled-AI-Director.html