Yes, TWILIGHT tells the story of a teenager who falls in love with a vampire, but far more can be read into it. The truth that Bella has fallen for the perfect, unattainable Edward Cullen leads to eternal love. The allure to this story isn't in fact the vampires, but the thought of loving your soul mate forever, in a quite literal sense.
While all girls can compare themselves to Bella's experiences, the new girl, the klutz, the unnoticed, Edward Cullen is every girl's fantasy, something to image about. As Edward returns his love for Bella, it gives common girls across the world the chance to hope and wait out for the man who will treat her like her queen. Thanks to TWILIGHT, more people are reading, and more are enjoying it.