Well, yes, it was quite a good movie, but it is based on a book of the same name written in the 60's. What i think makes the book better is that the 'zombies", if you will, aren't really brain-dead zombies. They talk to him, try to sexually lure him outside with their women and they stuck him, just like in the movie.
Now, the first version of this book put to film, The Omega Man with Charlton Heston, was an even better move. The nudity at one point was extremely unnecassary but hey, it was the seventies. The actual plot was not only more true to the book, but also i think the "zombies" were more organized and just infected people who thought they were the next step in evolution, which, i think, makes them more frightening as they stalk him set up traps for him, and as they kill those he cares for. The only thing missing that i htink I Am Legend really did so incredibly well with, is like what you said PJ: loneliness. Charlton Heston's character is a little more b.a. while Will Smith's is exactly the kind of person everyone would become in such a situation, attached to movies and talking to statues in stores.
So yes, i agree with you PJ, it was a good movie, and if you did like it and you're curious, try out The Omega Man. It, also, is a good adaptation of the book and just a good movie.