Not sure...
I experienced some lag like others have mentioned... but I also experienced something much worse that may only be affected by my computer or something, because I didn't see other people mention it. I had a big problem with the controls siezing up. Like, when I'd be running in a direction, many times the character would continue running even when I had let go of the keys completely. It seemed to become more of a problem the longer I had the key(s) pressed. I also had a problem with this and shooting. Sometimes my gun would get stuck firing if I clicked to fire too quickly, and it would just keep firing. Which made the game pretty much unplayable for me. My character would run straight into zombies (an unfortunately predictable plot), gun blazing, and me without a way to correct the fact that he was being eaten alive. I had to quit at the outdoor silo where the zombies first attack... just couldn't play under those conditions.