I will confess that I have never actually been able to get through the book - I always found it difficult to get through, even though the subject matter and themes are right up my alley. Also the clusterfuck that was Mary Shelley and Percy Shelley's personal lives are just so much larger-than-life that it almost doesn't seem real.  But this version is great, and seems to definitely take more from the book than previous films. It's still really influenced by previous film adaptations. I think it will win awards for its gorgeous costuming if nothing else. The acting was top-notch, and Jacob Elordi steals the show.

Changes the film makes:

- Per the article I linked, the movie is set during the Crimean War, which pushes the time period to after Mary Shelley's death. 
- The ending is hopeful, and ends on forgiveness, rather than the bleak ending of the original novel. 
- ScreenCrush does a pretty good explanation of the ending: