I managed to watch two movie versions of this book before actually reading the book, and I have to say it's interesting that they both changed the same plot twist into a completely different plot twist.
In the movies, the girl he finds is a real girl (not a vampire), and there is a small community of humans living in bolt-holes in the hills. The "Legend" that Neville becomes is that of the saviour of humanity - his sacrifice enables the "true" human race to survive.
Meanwhile, in the book, he becomes the "vampire" (of sorts) for the "new" human race. The legendary figure who strikes while your innocent family is sleeping, and in the "morning" (evening) you wake to find your loved ones dead and surrounded by a pool of blood.
I'm not sure the final twist works in the book, though. It feels as if we missed out on some information that Neville should have worked out. I mean, if they were forging a new society, making scientific advancements and creating an armed police force (of sorts), surely there would have been evidence of this in the daylight? Surely Neville would have noticed things being repaired and indications that society was starting up again?
I can't help but feel the book needed a few more chapters to flesh out some of what was going on in those last few episodes.
Other than that, it was a fun read - a great way to spend a couple of hours and a pleasant diversion for killing time in an airport.
I'd be interested to see if anyone ever films the whole book - and to read some discussion on why all of the adaptations feel compelled to change the ending so radically. Does Hollywood feel we need to have more hope for the future? Is the book completely devoid of that hope, just because humanity (as we know it) ceases to exist?