I saw the press screening of I Am Legend recently. It's not bad. They've taken some liberties with the plot, the vampires (or dark-seekers as they are here) are composed of some of the worst CGI ever committed to celluloid and there's some drippily sentimental scenes but overall it's okay.
Will Smith is pretty good as Robbie Neville, showing his mental state gradually deteriorating due to his isolation -- in some respects the film is Castaway with vampires. The problem is the film tries so hard with the quiet scenes that they start to drag on and then the filmmakers overcompensate with the action scenes with bullets flying everywhere and explosions that engulf entire city blocks. (Admittedly it's only at the end of the film that this tendency gets completely out of control.)
The vampires themselves seem inconsistent in terms of intelligence and their physical abilities. And as I said the CGI is bloody awful.
The worst thing though is the ending. I won't give it away but be prepared for it to be nothing like the novel.
The people I saw it with all hated the film much more than I did saying that it had been turned into a typical Will Smith vehicle. But I think there's a simple antidote to that attitude. Whenever you think the film is getting a little too glib or is focusing too much on the action in order to make Smith look good just think how much worse it would have been if it had been made with the original choice of star. Arnold Schwarzenegger.