This looks neat.
Apparently based on the book by Richard Matheson, it ends up looking like a version that starred Charlton Heston, namely The Omega Man. We shouldn't forget, however, that there's an even older version titled The Last Man on Earth, starring Vincent Price in the lead.
If the trailer is accurate, the premise of I Am Legend follows that of The Omega Man and The Last Man on Earth. Namely, a plague gets lose. A good chunk of humanity is annihilated, while most of the rest...mutate. Standard zombie movie stuff, really, except that in Matheson's book -- and pretty much in the previous two movie versions -- things are more complicated. In both the book and the Vincent Price film, survivors mutate into vampires; Charlton Heston didn't face vampires so much as albino religious fanatics who can't tolerate daylight.
What makes all interesting to me, however, is Matheson's underlying question: If everyone has mutated, isn't the lone "normal" man the aberation? I can't recall if there are any other "normals" in the Price film, or the novel for that matter, and there are precious few in the Heston film. Again, though, the queston we keep returning to is just what is normal?