There are so many reviews and so much discussion out there of the Twilight series, but I just had to get in my two cents in case you'd written them off as pap for the very young. Actually, you're not entirely wrong, there is something a little bit pap-ish about them. They are certainly not the highest form of literature ever to grace the shelves. However, the good qualities of these books far outweigh the bad, and I must confess that I love them for two reasons.
First, I am thankful to Stephenie Meyers for writing on a level that works for such a wide array of kids. Her situations and settings may sometimes be a touch simplistic, but her characters are so beautifully drawn that readers really start to care what happens to them. This is another wonderful phenomenon, like Harry Potter, where I am seeing huge numbers of kids being hooked into reading by these books. Many kids, both good readers and poor, are telling me that these were the first books they ever read where they stopped noticing how many pages or minutes went by.
One little girl told me that it used to take her two weeks to read a short (roughly 150 page) book. She wasn't so sure about reading Twilight because it is so long (498 pages), but she was actually able to read it over a long weekend. She only stopped reading when her eyes were starting to hurt. When we had our booktalk about her reading, it was clear that her quick read had not hurt her comprehension in the slightest. That's a pretty engaging book if you ask me. She's also gone on to read the other three monster books in this series.
Success like this is invaluable to a struggling reader. Looking at a shelf full of big books, and knowing that YOU actually read, understood, and even enjoyed them is a huge thing for many of my kids. Lest you worry, I am happy to report that when this girl finished with Edward and Bella, she went on to read other books and series. This to me is the whole point of YA literature. If a kid happens accross just the right book at just the right time, it can mean a lifelong change in attitude towards books and reading. The trick is to keep exposing kids to different kids of books in hopes of hitting on that magic one.