Okay so to elaborate, twilight’s vampires are the most interesting because they are the most human. They do not lose their reason, they are not given an inhuman rage, they still look passably human. The only things that change are the enhanced abilities, the immortality, and the blood thirst.
Given those circumstances, the chilling thing is that Carlisle was the only (known) vampire to attempt to live without killing humans. It poses the question of just how close is each of us to being a monstrosity? How easily can we justify evil in the face of the things we want?
Beyond that, in the reading, one almost forgets that the Cullens are vampires. They contrast between them and the other vampires Bella meets with is startling. It asks us if what makes the monster is not monstrous actions (most of the Cullens have made errors) but the lack of resistance to temptation? Is the monster osu temptation enough to taint the soul (as Edward thinks) or does the effort to overcome such an obstacle count as heroic (as Bella argues)?
It even asks us what it means to be human. Are the Cullens (though being not physically human) human in soul? Are the other vampires that prey on innocents? Are they to be held accountable for their actions, or give grace for circumstances beyond their control? What makes us deserving of grace?