Shacknews have this posted as the possible opening sequence to L4D2, it's an awesome bit of animation either way.

http://www.shackvideo.com/?id=15501

Article: http://www.shacknews.com/onearticle.x/60967

lol despite all that "Boycotting" the game still got 300% the pre-orders the first game got.

I'd say that's more of a trailer than intro tbh. I think the actual intro would have a followable "plot". It's still pretty cool though.

Tis awesome i ready know my favorite.