If you look at all the Disney SW movies, Rogue One is the only one that didn't break the SW universe or insult us like the other movies did.
It did fan service but it was cleverly woven into the story line. The DV scene can be written off, but it shows us a glimpse of a younger DV who was truly scary. (Of course, we got the good side version in Mandalorian, Season 2 finale with Luke). In a New Hope all we see Vader do is pick a guy up by his neck and throw him against a wall, force choke a commanding officer to prove a point, and fly the meanest Tie fighter (although we only see it flying in a straight line) in the entire movie. Not much really. Rogue One showed us more of Vader's capabilities.
Rogue One lines like K-2SO to Cassian, "Do you want to know the odds she'll use [her blaster] against you? It's high. It's very high," is very funny and is a reference to C-3PO and Han Solo in ESB. K-2SO "I've got a bad felling..." Jyn and Cassian, "Shhh" is also great. K-2SO truly makes the film fun and keeps it moving along. No K-2SO and this movie is very different. Back-pack guy and blind guy are great characters as well. While getting a bag put over blind guy's head, "Are you kidding, I am blind!"
Rogue One provides plausible explanations for how the DS was so easily blown up in A New Hope and a plausible explanation for how they received the blue prints to begin with. Introductions of new ship designs (Tie Striker, Krennick's Shuttle, and U-Wing) that are very obviously part of the SW universe. And let's not forget Vader's Castle that fans knew about from concept art and Expanded Universe comics. So to see it in movie form was awesome!
AND, let's all admit it - we all wanted to see the "Rebel spaceships, striking from a hidden base, [win] their first victory against the evil Galactic Empire" (A New Hope crawl). No victory comes without a cost. The cost is; everyone we came to know and care about in the movie dies. We knew it was coming because they had to have a plausible explanation why we never see any of these characters in any other SW movies.
The Force Awakens, Solo, and the other movies did fan service that was so in our face, as if none of us fans would get the jokes, that it was insulting. Rogue One didn't insult us, didn't break the SW universe, and provided plausible explanations that fit A New Hope. To that end, it worked well as a prequel.