Before the movie there was the book. And the book is the root of all evil...erhm...awesomeness that was then transformed into a movie. Many people skip over the book and watch the movie, which isn't getting an Oscar nominee any time soon, but it was a decent movie that reached its audience and made lots and lots of money. Twilight's true power lies in the books themselves. The saga transports girls and taps into all of their primal desires: to be loved and loved in return.
Twilight allows the book to be commercialized. Actors give characters a face that allows studios to create merchandise like Twilight party favors, and posters. Movies also reach a greater audience than books do. For some reason, many people don't like to read. They associate reading with schoolwork and boredom. The problem is that they're reading the wrong books. Twilight originated as a book so there was no way other than fan art to create merchandise to sell and make a greater profit. Being the capitalist society that we live in, there was no other place for Twilight to go but the movies.
The first three books especially transport the reader to a different world. With a simple language, anyone with a middle school reading level can enjoy the books. There is consistent action (minus Bella's whiny period in New Moon) and danger that makes your heart race and get you addicted.
Meyer's vampire folklore differs from industry standards. Her vampires go out into the sun and essentially have every day lives. One of the reasons to read the book is to explore this new world within our world. These vampires share similar qualities with other vampires and it's interesting to see where Meyer takes the other folklore. Granted she may have gone too far with Renesmee, but she sold it and supported her ideas and people loved it.
Another reason why girls love the Twilight series is the boys, duh. Edward has the tortured soul that taps into every girl's motherly instinct. We want to take him up into our arms, cuddle with him, and make everything all right.
Same goes for Jacob. Besides the fact that he's drop dead gorgeous (in our minds and as portrayed by Taylor), he's the best friend that every girl wants in a guy. Someone to talk to and spend nights with. He's warm (what girl isn't cold, seriously), and he goes to the ends of the earth for Bella. Granted its because he prematurely imprinted on Renesemee, but that's another story.
Besides all those reasons, the real reason is how girls can easily identify with Bella. They share a connection. Every woman has been torn between to guys, loved someone, and lost them. They've had to balance friends with a relationship. All Twilight does is show one girls way to handle being a teenager.
When people put down Twilight to fans, the best way for you, the fan, to debate them is to remind them of how the book is easy to read, involves love, danger and heartache. Don't forget how identifiable Bella is. Don't forget to tell them to shut up and read the book before they talk.
