Will Smith played his part quite well. I was amazed. The first two thirds of the movie were great, the abandoned New York, his daily routine, Neville slowly losing his marbles while trying to maintain normal human interaction by talking to mannequins, the night-time terror and screams.
The infected disappointed me, though. Mindless savages. Plus they looked remarkably like the robots in "I, Robot".
Then the woman and kid arrived. The movie went down-hill after that. It seemed like somebody noticed they were running out of time, so they wrapped everything up with a nice, neat Hollywood ending. The main character - soldier, scientist, a polymath - figured out a cure just as the other characters arrived, apparently sent by God or some higher force, spouting crap about how everything is connected, a plotline that was never even hinted at in the rest of the movie, and then died protecting them from the evil monsters, so they could deliver said cure to the remaining humans.