TL;DR - Despite some weird choices and missing details, this is a great movie.
The first of the standalone, spin-off, non-"Episode" Star Wars movies has been released! Rogue One sits in a territory of the timeline that is already being effectively mined by the animated series Star Wars Rebels: the period between Episode III and Episode IV, when the Empire is spreading and gaining power, and the Rebellion is still a scrappy little thing seeking its first big success. It focuses specifically on the small team of misfits that pull together against all odds to steal the plans to the first Death Star. In fact, (spoiler?) the movie takes us right up to the opening second of A New Hope, and features various cameos from that film's cast of characters - sometimes even going so far as to include creepy computer-generated recreations of the actors, or actual footage from the movie.
One of the more interesting things about Rogue One is that it gives us a different perspective on the Rebellion than we're used to. The original trilogy of Star Wars films is fairly black and white: the Rebels and the Jedi are the Good Guys, and the Imperials and the Sith are the Bad Guys. Sure, there are Han and Lando, who do questionable things, but they're the exceptions that prove the rule - a couple of rough and tumble dudes who are ultimately transformed and choose to join the Rebellion when they see it's the right thing to do. The Alliance itself is presented as a kind of monolith - a group of good people united to do good.
Things get a bit more complex in the prequels, as these films are the story of good things going bad - a Republic rotting from the inside and becoming an Empire (sounds familiar!), and a great Jedi falling and becoming twisted into a Sith Lord. But still, there's not a lot of gray area; Anakin and the Republic are good, and then a switch is flipped and they are bad.
What Rogue One gives us is an Alliance that isn't as allied, or as good and pure, as what we've seen in the past. These Rebels are fractious, with their own internal politics, intrigues, and warring factions. One of the first Rebels we meet, Cassian Andor (Diego Luna) does very questionable things in service of the Alliance. So questionable that he himself cannot look back at them, and must always move forward, trusting that the end will justify the means (which is a pretty morally and ethically shaky stance for a Star Wars hero). Later, at a Rebel council, we see how at odds the various heads of the movement are, and how easily the whole resistance could have fallen apart in despair and hopelessness right at its beginnings. But hope is what the film is all about: hope that we can see our loved ones again, hope that we can redeem ourselves, hope that we can make a difference, hope that we can somehow stop the darkness, no matter the cost. The "New Hope" from the title of Episode IV starts here - is born here, with the selfless and desperate actions of a group of people thrown together by fate (or the Force?) who seek only to stop the rise of the horrible, destructive, all-encompassing power of the Empire and its terrible new weapon, the Death Star.
Another interesting new perspective that Rogue One gives us is a view of the Star Wars universe through the lens of the ordinary people in it, instead of through the lens of a heroic prophesied Jedi. In fact, for the first time, this is a Star Wars story that has no Jedi in it at all. Donnie Yen's blind mystic warrior, Chirrut Îmwe, appears to be at least Force-sensitive, but as his close friend and partner, Baze Malbus (Jiang Wen), points out, he is no Jedi - because there are no Jedi anymore. Despite that, a faith in the Force flourishes among the Rebels, and it is much more like a religion here than it has ever been in the other films, where it was more a super power than anything else.
(Time for a plot summary! Mild spoilers follow.)
The central character of the film is Jyn Erso (Felicity Jones), a girl orphaned by the Empire, raised by a rebel even among the Rebels - the warrior Saw Gerrera (Forest Whitaker) - and then cast off into the world to fend for herself. Jyn believes in little except her own survival, and is resigned to the world the way it is - under Imperial control - until she has hope kindled in her again by a message carried by defecting Imperial pilot Bodhi Rook (Riz Ahmed). The message is from her long-lost father, Galen (Mads Mikkelsen), and it reveals that he is still alive, still loves her, and is not truly the traitor he appears to be. In fact, he has hidden a fatal flaw in the heart of the Imperial superweapon he's helped build, if only the Rebels can acquire the plans, and find an opportunity to exploit it. (It's a pleasing revelation that the design flaw in the Death Star was actually put there on purpose by the Rebel sympathizer who was forced to help build the thing.)
Even speaking as a die hard Star Wars fan, I have to admit that the series has never been big on complex characters or deep characterization. Anakin/Vader, as examined over the course of six (now seven!) films, probably ends up being the most complex and deeply realized character in this universe, despite the fact that he starts out in A New Hope as little more than a mysterious black-clad uber villain (albeit the daddy of them all). That being said, The Force Awakens made a successful attempt at deeper characterization, especially with Finn and Rey. Rogue One makes that attempt again, but it goes less well. Part of the reason is simply that there are so many characters, and so much story to tell, that there's little screen time available to devote to backstory and development for them all. By the end of the movie, I didn't feel like I'd really gotten to know any of our main cast. We only get the barest glimpses at their pasts and motivations. Jyn is the person we learn the most about, and I still felt like I was missing important information about her. The good side of this is, we want to know more about these people. They are intriguing, and clearly have fascinating pasts. I'd particularly like to know Captain Andor's story. He clearly has done some horrific things for the Alliance, and they haunt him.
Another good thing about this big cast: it's quite diverse. We've got a woman as the main character, accompanied by a Hispanic man, a black man, a couple of Asian men, and a Pakistani man. The people in charge at the Empire are white, but it seems clear that there's a point being made there - they're Nazis, after all. The Alliance has a lot of white guys, too, but they also have women, aliens, and black and brown people on their ruling council, as well as black and brown people among their ground soldiers.
Probably the greatest character in the film, however, is not any of the humans or aliens. It is instead Captain Andor's sidekick, the reprogrammed Imperial droid K-2SO (Alan Tudyk). The droid is a sarcastic, pessimistic, wise-cracking misanthrope, and it's hilarious and fantastic.
More mild spoilers: one of the things I found most disconcerting and odd about the movie was the decision to use computer technology to resurrect Peter Cushing so that he could reprise his role as Grand Moff Tarkin. Similarly weird was the inclusion of Carrie Fisher's Princess Leia in the final shot, made young again through computer technology. This was very distracting and totally unnecessary. The filmmakers could easily have found actors who looked and sounded like Cushing and a young Fisher and put them in the roles. We're smart people, used to different actors playing the same part; we would have been able to figure it out.
Rogue One is a Star Wars movie that takes a hard look at the filthy reality and the hard costs of war. It is a dark and a brutal story, but it offers us the promise that with these peoples' many sacrifices, a terrible evil will be destroyed, and future people will live in freedom and peace. And sometimes that's the best we can hope for.