Got a chance to see Rogue One over the weekend. I liked it, but didn't love it.
I'll start with the positive. The set pieces were gorgeous. The long action scene at the end was great. The cameos were cool. The way the film "expanded" the Star Wars universe as Bosk hit on above is true as well, and I really appreciate that. And yes, for the most part, the generation direction of the narrative was really interesting. We saw a different side of the rebellion, for sure.
I did think it suffered some of the writing issues of the other prequels, though, in the sense that, while the "big picture" was interesting, the way the plot moved from Point A to Point B sometimes left a little bit to be desired. The characters weren't fully developed. There were some illogical or otherwise circumstantial plot points that bothered me. For one, it makes the rebellion getting the Death Star plans look like an accident, or good luck, rather than a focused effort. This was a little bit disappointing. Also, I did think the movie was just plain slow. Until Vader's cameo, I was actually struggling to keep my eyes open. Maybe this is partly to blame because I'd read the Catalyst lead-in book, so I had already been made familiar with some of the film's early revelations (like the Death Star being powered by Jedi crystals).
But all in all, it's hard to be too disappointed. Rogue One is definitively outside the original trilogy and The Force Awakens for me, but I still enjoyed it more than any of the prequel films, which were better only in scope.