Frankly, I misunderstood the ending completely. I thought he said "the cure is in OUR blood" and that he meant the people who were immune. Which, you know, I thought was OBVIOUS. But he says "the cure is in HER blood" which makes no sense. Well yeah.. the cure for CANCER is in her blood, which also happens to be the cure for not being a zombie, but how can the cure for being a zombie be in the zombie's blood? How is this a sudden realization? It doesn't make any sense. Yes, in theory if you keep studying the zombie blood then you should figure out a cure. That's what he thought in the book until he realized there IS no cure. This is the human race.
As for the monsters, they were rendered ineffective by having their humanity removed. They were made into animalistic monsters, but also they can think logically enough about their opponent to plan and rig a trap, and they can love. But also they're pointlessly strong, can run straight through a steel door, and attack a glass partition by SMASHING IT WITH THEIR FACES instead of using a tool or a blunt object. They're clever enough to bite dogs to turn them into "dark seekers" instead of EATING them for survival, but they're not smart enough to get some guns to kill Neville with, or put on some sunblock and some hoodies and go out in the daytime. In short, they're plot-serving monsters with no consistency. So any "point" or poignancy is loss in the muddle.
They set up Neville as being a control freak doctor like Jack on Lost, so that his obsession with "curing" the zompires was more selfish than compassionate. Instead of his family dying of the virus, they die in the most astronomically improbable freak accident of all time - the only two helicopters in New York City smash into each other. They might as well have spontaneously combusted or choked to death on a chicken wing. They died first, unrelated to the virus, instead of dying last and giving Neville a reason to want to save the world. Now if he saves the monsters, his family is still dead. He might as well not even have a family to begin with.
I was almost right with my early prediction about how they'd end this movie. Except they left out the part where they build him a huge golden statue in Vermont. They should have done that, and had human kids running around the statue with bald creepy zompire kids catching butterflies. For he is LEGEND!