Clarifying my Left for Dead Thoughts

I received an email from someone talking about the AI Director for Left for Dead which will make it a completely new experience each time through and that it's worth the $55 bucks.  I'm sorry, but if the zombies come at me in 20 different ways, if the end result is the same, isn't it still only two hours of gameplay each time through?  I stand by my original post.  Valve should be ashamed of themselves for charging $55 bucks for this.  If the new content were to be free, then yeah it might be worth that much money, but we all know that Microsoft doesn't like to give things away on the marketplace.    This should have been released as an XBL Arcade title.