Did you notice the flaw in Eclipse about how Bella thinks of her life?
In the middle of Eclipse, Bella is listening to Rosalie talk about her perfect human life. She also made a comment to Bella about how miserable Bella's life on Earth was; and Bella came back right away and said that her life wasn't miserable. In fact, her life wasn't miserable at all!
And then at the end of Eclipse, Bella gives Edward a long speech about becoming a vampire, because all her life (18 years! hah!) she's always felt out of place, out of step, and fumbling thru life. And she knew that by becoming a Vampire that she would actually fit in, and feel good about herself.
I find that this flaw gives you the impression that perhaps Bella is too young to make such a huge decision in changing her life. Especially when she says that her human life wasn't miserable at all. For me, it is too bad that they couldn't find some sort of cure to make Edward human again!! Now THAT would be Cool!!!!