Word. I watched this Sunday and loved it. Even without the vampire element, the movie would still be superb.
I kinda want to read the book just to get more details about Eli and her past and the man who took care of her, etc... probably won't though. boo.
If you want to know a little bit more about the girl and the man's character, I would suggest going to imdb.com, searching for "Let the Right One In", and looking up the bulletin board topics for this particular movie. I didn't read the book for this movie as well but I gleaned a lot from this bulletin board in regards to interesting plot points in the book that were left out of the film. Although there are a couple of key plot points that weren't explicitly conveyed from the book, the film still stood out on it's own merits/interpretation. But once you learn how Eli came to be a vampire and her symbiotic relationship with the 'father-figure' man, it will make you really re-think about the love story between the two young characters and realize just how 'pure' their affection for each other is. There are more boundaries other than a vampire-human one that their relationship surpasses.