I'm on book 4 of the Twilight Series. I ended up finishing book 1 and 2 while in Ireland. I originally wasn't going to, but I ran out of things to read. While in Philly, I downloaded book 3 and 4. I originally only downloaded book 3 but then I realized I wanted to know how the whole series ended so I got book 4 too. I read the last chapter or so first. Just so you know. :)
Book 1 - Started out very slow. I really do not like the character of Bella and I can't fathom why anyone likes her. I could be clouded in judgement by both my dislike of the actress I saw in the previews of the movies and what I think about the author. I still do not think the author is a good writer. Without the movies I would have no mental image of any of the characters (and in reality, I only have a mental image of Bella and Edward because they were so heavily featured in the previews). I forget when it finally got decent, but I still wouldn't go so far as to call it good.
Book 2 - I liked parts of book 2. I'll admit that. :) I like the character of Jacob. I still don't like Bella and kind of hope she dies. Obviously she doesn't or else there wouldn't be a book 3 or 4. :) I have a huge issue with this love story though and what it teaches girls. Perhaps it is because I'm not especially romantic but in reality I wouldn't want someone to "love" me the way Edward and Bella "love" each other. Edward's also a bit of a drama queen.
Book 3 - I liked book 3. Still hate Bella, mostly dislike Edward but I did enjoy Jacob and the rest of that storyline. I also liked the struggle and how things were resolved.
Book 4 - I'm part way through (33%, thanks Kindle for letting me know that) and still hate Bella, think Edward is a fool.
All in all, the writing gets vaguely better as she goes along. I'm not a fiction writer, should I really judge? Sure, why not. I don't think she's anywhere near as good as JK Rowling, though. While there are definitely times where Harry is kind of a whiney baby, he's nowhere near annoying as Bella. Are they worth reading? Probably. If you're not me. :)