First things first, I am Legend is a legit film. I'm as surprised as you are. I know it's barely fresh (60%?) and some of the critics say it derails around the 3rd act but I disagree. This film is solid from start to finish. Will Smith is not really a Denzel-level actor but he gets the job done here. I was actually mildly disappointed the film didn't collapse like Saw, but I think my enjoyment of the film outweighs my disappointment.
The plot is almost the same as The Omega Man, the 2nd film based on the novel by Richard Matheson. Robert Neville is (as far as he knows) the last normal man on Earth. This is the end result of a lethal virus that killed over 90% of the World's Population. Those the virus did not kill turned into zombie-vampire like beings. Neville searches for a cure in NYC while fighting off the infected as well his increasing loneliness and isolation.
My main problem with this film is that the infected are all CG. It made it look like a video game but I guess to the average person this is "cool" and they don't think about video games. I felt the infected would have worked better if the film had stuck with actors in makeup but I suppose CG is the wave of the future and whatnot. At least I got to see what Resident Evil would be like if Will Smith starred in a game.
The only thing that could've made this film better was if Will Smith uttered his trademark phrase. I would also have accepted a music video / rap song about I Am Legend; it totally could've been the next Thriller!
Joking aside, I would definitely recommend seeing this film. The third time's the charm (sorry Vincent Price and Charlton Heston.)
Also, while there is a Dark Knight trailer before the regular version, if you go to an IMAX screening you will get the first 6 minutes of the film. You'll get to see the Joker's henchmen rob a bank. Needless to say, hilarity ensues! This film looks great and I'm already psyched for this summer.