Uhmm...Meh.
I'll give points for the fact that it's related to Left 4 Dead (one of my favorite series of all time), but...
Was there a point to this?
I don't know what you were going for with this. Nor does it seem like it was even well drawn enough to keep my attention. The sound on this video is obnoxiously loud, despite my volume is at only 16%. It seems like you were just bored and made something random and posted it here. Which, in turn, is going to annoy the rest of us. It's fine to make stuff up for your own enjoyment. But if it's not quality work, keep it off Newgrounds.