I read this book a couple years ago, and then our book club decided to read it, so I just finished reading it again. It really is a great book - the mechanics of the time-traveling aspect are done well enough that scifi fans will be kept interested and happy and the love-story aspect of the book is extremely well thought out and interesting. It's the only example of a book I know that puts these two genres together so well. I highly recommend the book!
The alternative, you may know, is to try to save time by just seeing the movie. You could do this, you might even like the movie, but be warned that it is considerably less interesting and dynamic than the book. Watching the movie (which I did within 12 hours of finishing re-reading the book - that may have made me hyper-sensitive to changes) I felt like they had taken this complicated and adult-themed book and made it into a movie a 13-year-old girl might enjoy. My main problem was that Clare, who in the book is smart, logical, and self-possessed, becomes the stereotypical whiny, illogical girl in the movie. In general, anything in the book that required thought or complex emotion - things about the characters that might not be entirely wholesome or comfortable/cute get left out. So, see the movie if you like (especially if you've already read the book - just to jog your memory) but also read the book so you can appreciate how good the story really is.