If you've read the Twilight series, this is a must see. While I wouldn't say it was a "good" movie, it was very entertaining to see Catherine Hardwicke's interpretation of the novel on the big screen. They used a lot of original lines from the book, but made some good changes as well. There were a couple of scenes that weren't supposed to be funny that got a lot of laughs at the midnight showing, however...
If you haven't read the books, it's a tough call. The first half of the movie might be hard to sit through, as the pacing is kind of slow. The second half should keep you entertained as the suspense picks up. Also, if you're a guy, you might want to skip this one. I saw some pretty miserable boyfriends in the audience.