Even in movies zombies are rarely convincing. In general, it is very difficult to reach authenticity, because the behavior of zombies is usually adapted to the needs of the film. When speaking of games, it's therefore a logical reasoning to make them for a shooter faster, stronger and more flexible than in e.g. Night of the living Dead - because if they weren't, they would be an easy target. To make a truly authentic zombie game, you would have to make the player as vulnerable and helpless, as it would likely be in a real apocalypse without medikits, without firearms and being infected as soon as you get bitten.

Does anybody know the film Wasting Away? This film is an oddball comedy from the perspective of zombies themselves. It is quiet funny and a quiet interesting approach. I tell you no secret that this is a niche, which is not yet exploited.