The best zombie movies use the shambling reanimated corpses as allegories. George Romero, the father of the dead, used zombies to represent everything from racism to consumerism as well as demonstrating that the most dangerous thing to humanity is ourselves. Pretty powerful considering the antagonists are as silent as they are numerous.
The worst zombie movies, on the other hand, use zombies to represent capitalizing on a trend and making as much money as possible before writing off their losses when the tax man comes. The movies that go this route end up being as mindless and slow as their subject matter.
It is safe to say that there are far, far, far more examples of the latter than there are the former. This could have been the top ? just based on the SyFy channel alone.