Admittedly, it's not the worst book I've read. Not even the worst book I've read voluntarily (though, it competes for the title, and might be adjusted later). But it's well within the worst one percent of all books I've read.
The book is about a parodically clumsy but otherwise Mary Sue-ish girl named Bella (which means "pretty" in Italian. Already there, you know what direction this is going to take) who moves from Phoenix (which she loves) to some ultimately depressing town in Washington (which she hates), for no apparent reason at all. She has no defining character traits, apart from a clumsiness that borders on retardation.
In said depressing town, she meets a boy named Edward, who is described as being "perfect" on literally every other page*. Edward, who turns out to be a vampire, has no personality either (apart from the "perfectness"), but he is a stalker who regularly talks about eating or harming Bella. To be fair with him, even though Edward doesn't really harm her much, she manages to do it annoyingly often herself. The two somehow end up as a pair.
Even though Bella is repeatedly described as a bland girl, all the non-vampire, non-family males MENTIONED in the story shows a love interest for her. She never turns any of them down, but just says "some time later" to everyone, which again makes up for more intrigues involving her vampire boyfriend. All in all, this book would have been 300 pages shorter if it weren't for all the "but then you said to him..." and "I thought you didn't like me...". Due to all this drawn-out-ness, it's almost impossible to find any sort of storyline for the first 350 pages of the book. At that point, a random villain appears out of nowhere. There is a lot of fuzz about him, Bella manages to almost kill herself despite everybody explicitly telling her not to, but luckily, perfect Edward manages to save her at last. The villain is never heard from again, and Bella and Edward go to prom together. Cue end credits.
Then, onto details and my opinions. As many have mentioned before me, the vampires. All I have to say, Bram Stoker would be crying. Loudly. Super-senses and -strength, OK. Bram said that too. However, random magical powers, beauty and that goddamn sparkling almost made me puke. Everybody, go read "Dracula" now, so that if civilization is lost tomorrow, the last image we'll have of vampires won't be those... mannequins that Meyer describes. Mannequins or statues; the vampires are described as cold, hard, emotionless and generally good-looking. Bella being in love with one sounds an awful lot like Agalmathophilia (Wiki it).
Despite all the slate it gets, this is apparently the best of the books in the Twilight series. I have read summaries of the rest, and I have to say, I'm only willing to read them if I have to. Should I, so you won't have to? Give me your opinions on this review and answer.
*I did a little research. I asked my calculator to give me 30 random integers between-and-counting 16 (the first page Edward appears on) and 434 (the last page with text on in the book, not counting the previews of the next book), and 18 of those pointed me to pages describing Edward perfect looks, super-senses or Bella's heart rate speeding up by mention of his name. My sister, who is a fan of the series, judged and overthrew a few of these 30, but we still ended up at 18. Percentage-wise, that is 60.