I recommend reading the book before you see the movie.... the movie didn't do the best job of reflecting the quirkiness, fun, and intensity of Edward and Bella's relationship. If you see the movie first, I think you wouldn't really run to read the book.
Also.... this a low-budget film. The action sequences are nothing like what you might be used to with Batman or SpiderMan movies. :) So it makes some parts a little cheesy.
But overall, if you enjoyed the book, you have to see the movie, even just out of curiosity to see how they portrayed such an intense love affair.