Most people focus on the fact, that there was not enough "backstory" for characters to like them and make their deaths meaningful or impactful and the movie was just non-stop action and really did not bring anything "new" to table..

But here is the thing:The whole Rogue One band was fellowship of unlikely "heroes" that got together to do one job, that in the end everyone in the audience knew will mean their life. So why spend screen time on backstories for them or to reinvent the wheel, to make their deaths more impactful and fit the SW formula, when instead you can spend more time to revel in their deaths and make the deaths equally impactful, and also make their deaths impactful because of their current heroic actions, instead of them being motivated by some long time past grudge.

How much of a backstory did characters of Saving Private Ryan get, anyways?

But nor to digress, to point two: this is no happy ending light over dark Star Wars story with heroes that will save the day with their perfect smiles or live to fight another day, because it is their destiny, so they can smile their perfect smiles. This is simply movie about the less glorified, knee deep in blood struggles of the rebellion against the Empire ruthless oppression. It is set 19 years after Ep3, so nobody probably even remembers Jedi and The Republic, because most of those that do are either dead, or so underground, that they cannot tell people about the Jedi anyways. So what hope people that are against the rule of the Empire have? To fight and sacrifice everything, because no one else will do it or just accept the state the galaxy is in now. Even the Rebels were not so sure at that point, which path to choose. And that is what Rogue One was about in the end.

And the final scene, when Darth Vader just mercilessly and effortlessly butchered the whole ship was the final taunt from Edwards towards people that went to see "happy" SW movie, where heroes save the day. That scene felt so out of place and raw, yet so in tone with the whole movie.