I've read the book and consider The Omega Man as one of my favorite movies.... I didn't like this rendition of I Am Legend.
The power of the orginal story lies in two parts.
1. The "vampires" aren't just monsters. They maintain human qualities and begin to assemle as communites and bascially contine to act as human beings under new conditions.
and
2. Robert Neville, although the last "man" alive, realizes that he has been terrorizing and murdering the "infected", and that he is the outsider that is no longer wanted. He essentially becomes the reflection of what he's fighting against: A threat against mankind.
This didn't capture either of the above points, they actually go opposite against both points.
They completely make the "infected" as inhuman as possible and Will Smith doesn't really try to eliminate any of the infected... unless his life absolutely depends on it.
By removing the psychological dynamics in the original story Hollywood proceeds to give viewers another fluff piece with no real substance.