If you look closely at the videos you can see the zombies 'float' along the floor, like you get when in a mmo and you get major lag. Thing is its very disguised when you have hundreds of zombies running at you.
Not really noticed this in game.
Try playing it.
so yeah ill wait till weekend deals.. x] played it on my brothers account!

it's kinda the same as cs1.6 compared to CSS
