Considered on it's own, I Am Legend is fairly solid. The desolation of an abandoned New York being reclaimed by nature is a powerful image, and Will Smith does quite well in the role of an isolated and slowly losing it Robert Neville. Definitely his best performance, and perfect for a character study such as this. CGI vampires was a poor choice, though, but might've worked if they had been kept in the shadows, away from full view. The absence of Ben Cortman was also a bit of a let down, but having him in there wouldn't have made sense in this version of the story.
The new ending totally alters the meaning of the original story, and the meaning is where the title itself ultimately comes from. Neville in the novel had become to the new vampire society what vampires (and really, all traditional monsters) are to us; he was a mythical, unknown, and dangerous entity that crept around in the daylight, killing them in their sleep. He was a legend, a story that would be used to scare future generations of vampire children. Will Smith's legend was that he found the cure, and that isn't anywhere near as profound.
"Don't worry about a thing, cause every little thing is gonna be all right. Rise up this morning, smiled with the rising sun. Three little birds pitch by my doorstep singing sweet songs of melodies pure and true."
Bob Marley is awesome.