High quality period piece although the book is supposed to be even better. I haven't read the book so maybe you will want to do that first. Back to the movie. The cast is superb and the story is compelling. What more do you need? The story has great characters, and the the cast brings out all their emotional interests. The story unfolds in a series of flashbacks as several characters are unwilling to share what happened during the German occupation with intrepid writer Juliet. This works well to build suspense around the overall mystery. Juliet is dealing with her own tragic war memories which drive her character's choices. Guernsey is like a character too and will probably be swamped with tourists in the near future.
As far as the present, we can all have a very pleasant journey there by just watching this great movie.