I assume that if you are a person who hasn't been living in a cave for the past decade, you probably already know about Twilight. There is a good chance that the average person today knows more about the backlash and hype surrounding the book than they do the actual book. There is quite a bit written about the possible political and social ramifications of the book, and I have heard many accusations that the book provides a very negative example for young women of what a relationship should be like. All of that, and more, is probably true. I have to admit that some of the subtext is pretty disturbing, especially the equation of sexuality with predation, and the easily inferred concept that it is men's potential for violence that makes them attractive. But to really get into all the possible ramifications of this book would take a long time, and would require quite a bit of deconstruction that would go outside of the book itself. I don't think that this book quite deserves to launch a deconstruction of the entire history of gender stereotypes.
Dealing with the book just by itself, we have a fairly routine young adult romance novel, with a vein of the supernatural. There are many young adult books with romance, the supernatural, and vampires. One of the most surprising things about Twilight for me is why this particular book has become so popular: the basic storyline has been done many times before. And Twilight doesn't do it particularly well. The basics of a novel are plot and character. The book is 500 pages long, but for the first 350 pages, it doesn't actually have a plot as such: there is no actual dramatic tension or movement, as much as there is Bella and Edward mooning over each other. In the hands of a very exceptional writer, a bare description of emotional discovery can be interesting enough. The final 150 pages has a plot of some sort, but at that point it comes across as tacked on. And, if the book is to succeed without a strong plot, but instead is to depend on characterization or description, it should be pretty good at it. Instead, we have two characters who go into rhapsodies of love, without having any explanation of what makes them appeal to each other (or to us, the reader). Bella Swan never displays any interest or insight into the world around her-- we are informed that she reads books, but her conversations and actions never display the slightest bit of intellect or initiative. Edward Cullen is interesting because he is super-powered, and refrains from using his vampiric powers to harm humans--- but he too never seems to display much insight into the world, despite having a 100 years of experience at living. The conversations they have with each other are not particularly interesting or romantic, even within the conventions of a romance novel for teenage girls. And these are the primary characters-- none of the secondary characters shows any individuality at all. Bella's father says some "concerned father" dialogue. Mike Newton says some "teenage guy with a little crush" dialogue. Bella's female friends...gossip a little. In other words, the book has little plot, little characterization, and even less connection between the two.
Of course, the shortcomings of the work as a narrative are not independent of its social implications. While it wouldn't be necessary to have Bella launch into long speeches where she dissects the world of politics, it would make her a more interesting character if she had some type of thoughts or interactions with the natural or social world around her. Instead, her existence is confined totally to her love for a supernaturally perfect man, and that is both problematic socially, and doesn't make for that entertaining of a narrative.