I think a lot of you miss the entire concept of a vampire.
The scariest vampires and the most well fed vampires, are one who use their charm (and looks I guess) to lure women into their grasp. Vampires have always been, in a strange way, alluring, sexual and strangly charming.
This has been done far before Twilight. As a matter of fact, most vampire books I've read have had a female who sees a vampire and immediately falls in love with him. The vampire will either kill her or not kill her (depending on the novel).
Also, vampires falling in love with humans is nothing new either. I've read books about vampires falling in love with humans. It's actually rather sad because their human lovers also die of old age and the vampire is then left alone again. It's sad, unless the vampire turns the girl/boy to a vampire, then they live together.
Howver, in Twilight... Well, there is some interesting stuff, but it just didn't translate well to movies I guess.
I could see why they sparkle. We humans are drawn to shiny stuff, maybe if you're hiking in the forest, and you see a person sparkling like diamonds, you'd approach them. You'd then be dead because the vampire would kill you by then.
Another thing I think is interesting is the fact that the vampires can't just have a little blood from a human, they have to go all or nothing. If they only drink alittle, they'll turn the person into a vampire (which may not always be desired). If they drink it all, well the person will die.
My 25 year old brother has read ALL of the books and actually found them interesting. The most interesting thing he found was that Edward, the male vampire, cannot get too excited around Bella or he might kill her. If she cut her finger, if she kisses him too much, if she touches his weener, all these things could push Edward to get overly excited and lose his control and then BYE BYE Bella.
So while interesting ideas are there, it is sad it didn't translate well.
And no, I have not read any of the books, but I have seen the movies. (Saw it out of curiosity and now have to finish them all. I can't leave sagas uncompleted, it bothers me. >_<)