I Am LegendStarts out legendary, and ends up being forgettable.
I was really excited about this movie, the previews looked amazing and the concept was fantastic. While I was ultimately disappointed with the final outcome, I can't say that the experience was a total loss.
The basic plot is this: A doctor devises a cure for cancer, by use of "re-programming" the virus to reverse the effects, this cure is actually a more modernized form of the Vampirism disease that we all know and love. For a time, the entire world rejoices and all is good, but after a while, the treated patients begin to show signs of the disease, and eventually the infection is spread throughout humanity, turning the human race into Vampires of sorts.
I would describe the infected as a crossbreed between Zombies and Vampires-- they have all of the traits of Vampires in terms of smelling blood and being harmed by sunlight, but they also exhibit traits of Zombies, being generally mindless and flesh hungry. It's an odd mixture, but it works with the plot. Genetically immune to the disease, Will Smith is left alone as the sole survivor of New York city, unaware of whether or not he is the last person alive in the world.
The first half of this movie was spectacular and filled with suspense, drama (via flashbacks), and comedy, all very well done. The acting is superb and the story is totally believable, and it was very easy to relate to the characters, all of which created a fantastic atmosphere explaining how the world got into the situation, how the disease spread, how different animals and humans are affected by it, etc. It really sets the stage for the rest of the movie to be awesome, and for a time, it is.
There is an amazing relationship between Will and his dog, Sam, who aids him in gathering food and keeps him as sane as possible, and is an instantly lovable companion. The movie is at its best when man and dog are together, alone in the city. The most gut wrenching scene in the movie is when Smith and his dog Sam fend off an attack from some of the Zombie-Vampires and their Zombie-Vampire dogs. The scenes that follow the fight are absolutely amazing, and if I could explain the spectacular drama without ruining the plot, I would, but alas, I cannot

...and it is here, at the climax, the finest point in the movie, that everything goes down hill. It's really quite tragic, because everything was layed out so well... it's actually more disappointing that the end was crappy than the crappiness itself, if you catch my drift. A random-assed girl is introduced out of no where, apparently also immune to the infection, and has somehow survived long enough to travel to and find Will Smith. The new random character finds Will Smith just as he is about to be slaughtered by a pack of Zombie-Vampires.
At this point, it is evident that some dumb ass got ahold of the script and decided to diverge from the dramatic plot that movie was running on, and instead turn it into a story about faith and God etc. When Will Smith asks the random girl how she found him, she responds, "God told me to find you... The whole world is silent, if you listen, you can hear God speaking to us!" I almost barfed.
Luckily, Will Smith denounces this almost immediately, which is fine, because at least the jacking off to Jesus is only a character's perspective, and not the point of the movie. WRONG. Will Smith eventually accepts Jesus into his heart and commits Zombie Jihad, and in a spectacularly pathetic final scene, sacrifices himself to save the girl and the boy, while saying "I'm listening now...". Yuck.
Okay, let's say you don't have a problem with that. Maybe you think God speaks to you, too, and have your own cult. So, you see no problem with that. Fine, fine. But the movie doesn't stop there with the sucking. The plot starts to get more holes in it than my grandpas underwear, and nothing is really explained fully.
In one scene, Will Smith talks about how a Zombie-Vampire exposes himself to sunlight willingly, showing signs of intelligence, but passes it off as hunger making the creature ignore its instincts. Later in the movie, the same Zombie-Vampire sets a VERY sophisticated bate and snare-trap to catch Will Smith, showing us that it obviously does still have intelligent function and is more than just a mindless zombie beast. This aspect of the plot is abandoned and never brought up again or explained after this point. Sigh.
The movie loses direction and instead of focusing on Will Smith's struggle and the actions of the Zombies, it focuses on plot devices that were only introduced after the first 60% of the movie (i.e. stupid new girl and her prospective hope of finding the "last stronghold of civilization").
Everything that was great about this movie is destroyed and lost about halfway through the film. Nonetheless, I am still going to recommend seeing it, because the first half of the movie is a great flick, and totally worth seeing. Just brace yourself for sappy cliches, terrible writing, and plot holes just after you experience the best parts of the movie.