Set just before the beginning of the original "Star Wars" movie (you know, the one from 1977 that didn't need a number to tell you where in the sequence it was?), this tells the story of Jyn Erso (Felicity Jones), the daughter of a Galactic Empire scientist partially responsible for the creation of the Death Star. She reluctantly joins the Rebellion - to find her father (whom she thought dead) and to recover her father's name.
It's a war story, lots of people die. Comedy is inserted in the form of K-2SO (played by Alan Tudyk, who's been typecast as a robot in this rather modern type trap) and Chirrut Imwe (Donnie Yen), a blind would-be Jedi Knight. Yen makes for the best action scenes, and has surprisingly good comedic timing. He's also quite charming. I've liked Jones in the past, but didn't really think she was particularly good here: I didn't think she showed the strength of will needed to enter a war as she did, despite her character's back-story. Diego Luna was fairly good as her partner in crime.
There are endless nods to hardcore fans of the original: for example, one of the characters bumps into a belligerent person and his friend on the street and barely avoids a fight. Fans of the original movie will recognize the two characters from the cantina on Tatooine that tangle with Luke and Ben. There are dozens of these easter eggs, but I found them more distracting than entertaining. Can't these movies move forward instead of constantly referencing the past? Of course that's a bit silly to ask of a prequel ...
This generally avoids the retconning idiocy that Lucas inflicted on the world with "The Phantom Menace," "Attack of the Clones," and "Revenge of the Sith" - ie. the facts actually fit with the movie that nominally follows it. Overall a better movie than "Star Wars: The Force Awakens," but that's not saying much.