Plot It’s been three years since a killer virus struck Manhattan. Those who aren’t dead have mutated into vampire-like beasts. All except Robert Neville (Smith), a military scientist desperately looking for a cure.Verdict While the sun shines, it’s a four-star thriller with a superb turn from Smith. When the moon rises, it’s a two-star horror cartoon with some of the worst FX we’ve seen all year. So, really, it has to average out at…