Will Smith is pretty much forced to take the reins in I Am Legend, considering he is supposed to be the last person alive. Although Smith is a good actor, he is not a great actor. When you are going to make a film where your main character is essentially the only character, you MUST have a great actor to fill the time. Tom Hanks did it in Cast Away, and John Cusack was able to do it in 1408 (<--review coming eventually), but Smith was not able to accomplish it here. His performance was not all bad, as there were parts where I felt truly emotional as Smith started to lose composure after a tragic event. (I'm trying not to give too much away, but you could probably figure out what happens). Unfortunately, the emotional performance only takes up 10 minutes of the film, and the rest of the act is quite boring and plain to say the least.
One very positive thing to say about this film is the overall look of this post apocalyptic New York City. Through the opening of the movie, we are brought around the city where grasslands have overtook the streets and animals walk where humans used to reign. These effects are rendered very well, especially considering the director Francis Lawrence has only directed one film before, and his expertise lies mainly in music videos. But the visuals are not perfect, which is clearly evident in the effects used to generate the dark seekers. The infected people look flat out silly, and aren't very scary. It is also very clear that the makers used complete CGI to portray them. It really took me out of the film.
All in all, I Am Legend had A LOT of potential in being a great film, but failed in more than one aspect. Try again in another 25 years or so with a better actor, and it'll work. My rating (5/10)