I really enjoyed both the book and the movie. I saw the movie for the first time a couple years ago and finished reading the book about a month ago.
Although there were comparisons, there were also differences, like the guy in Miami who's name was Richie Gatso in the movie was Tony Conte in the book. And Pistone's wife's name was Maggie in the movie and Penny in the book (I think it was Penny, I can't really remember).
I really love the movie, it's my 2nd favourite of all time, sometimes I say it's my 3rd favourite, depends on when I last watched it.
But the book is worth reading for sure I'd say.