I Am Legend isn't nearly as bad as the critics made it sound. It's actually pretty good - sort of like Castaway with monsters. Castaway's another movie that had an excellent first two-thirds, followed by a shaky final act. But to be honest, I didn't hate the ending of I Am Legend. I could have done without the nearly ten minute excerpt of Shrek - even Steven Spielberg shouldn't be allowed to get away with that kind of stuff any more - but in general I was able to suspend disbelief and go with the internal logic of the ending.
There's a lot of talk about how inherently likeable and amiable Will Smith is as an actor, but one of the marvels of the story was how aged and morally damaged his Robert Neville is by what he's seen and done. The usual moral calculus of zombie movies is inverted by the establishment of this Neville as a scientist and virologist. Despite some idiot claims by some reviewers, Smith's Neville doesn't start the movie hunting or slaughtering the monsters. Rather, he seems to be avoiding them as much as possible, and when he captures one, it's to test out a promising cure on the slavering thing which used to be a girl. Later, we see photographic records of each monster which he's captured and killed in the process of testing his serums. It's an unsettling moment, as you suddenly look again at your protagonist and see a mad scientist and borderline serial-killer in the place of a heroic castaway. It's all means to an end, but you can see that he's operating by habit and routine - that he's going through the motions of a plan, the soundness and righteousness of which he has mostly forgotten.
Smith's Neville lives so much on the surfaces of things because the depths have monsters. He moves from light to light, sealing himself up and locking down as the light goes away. He populates his locales with manikins, and carries on conversations, and has lost his way among them to such an extent that when one is moved out of its place, he becomes confused, violent, and makes a terrible mistake.
Smith's Neville is a man so morally fractured by his failures and successes that he's more a mosaic of partial personalities than a whole man. Inside his townhouse, he's a loving family man - to a family consisting solely of his dog. Inside his lab, he's a rigorous scientist. In his open-air office at the end of a dockside pier, he's a parody of a bureaucrat, waiting for other survivors, of whom he's given up all other hope except for those few designated hours by the river. When the shutters close, he hides with his dog in the darkness. The only thing holding his parts together is the only other person in his life - his dog Sam. Sam is the one thing holding his life together, and when she dies, then Neville goes smash.
The movie goes smash a bit as well, although not so much that I wasn't able to enjoy everything that followed. The CGI was terrible, not in that it was technically bad - although it didn't impress me all that much - but rather that it is a terrible temptation to cinematographers and directors. CGI is a cheat, a shortcut. It requires no discipline on the part of artists, and thus it relieves the pressure on decision-makers to make choices, to commit to one action at a time. CGI allows blazingly-fast action sequences, and the faster they go, the cheaper the cost, because all of that blur can hide all sorts of shortcuts and cheats and render-tricks. Instead of showing one single clash, with a small and well-defined set of actors or objects in motion, CGI allows and almost seems to demand a blur of mobs in motion. Blur isn't interesting, and mobs multiplied by cut-and-paste are basically expensive wallpaper, and about as threatening.
There are honestly cool things in the last third of I Am Legend. Every single one of them would have been better with at least half of the CGI animation cuts excised. I don't know why they thought they needed spectacle beyond the scenes of Empty Manhattan. Those were far, far more powerful than any of the swirling killer-zombie cuts of the last third. The head monster was most alarming when he was *still*. Whenever he moved, he became an effect, and then action wallpaper.
Too bad. American movies aren't going to get better until they fire half the animators, and send the directors off to make films with real-world special effects. Real explosive squibs and stuntmen teach a certain respect for the craft which isn't much different from fear. But fear teaches. Ask John Landis.