I'm going to review all of these together. They were originally published as four separate books, but were re-issued with two novels in each book. They were written in the early 90s, and the author just released a new book in the series this month (I'm reading it right now).
I'd heard good things about these books. A lot of things in them are similar to Twilight. Not nearly as good though. I did enjoy the books, but think someone a little younger might enjoy them more. The relationships are not as intense as in Twilight, but it's the same type of thing - vampire and human girl in love. I don't really know WHY Stefan loves Elena though, she's pretty stuck up and spoiled. I did like her friends though. I liked the character of Damon also - Stefan's brother who also wants Elena. I thought the first two books were the strongest of the series. The fourth was mostly told from the point of view of Elena's friend.
I was hoping for a little more with these books, but they were quick reads and I did stay interested. I even got a little spooked a few times. I just didn't feel as connected to the characters as I would have liked to. If I weren't comparing them to other great vampire young adult books that I've read recently (Twilight or Vampire Academy), I might have liked them more. I think that young teens might enjoy them more than I did though.