Force Awakens, even if it was for nostalgia's sake.
Rogue One tries to be a hardened, serious war movie.
Well, the problem with that for me is that Star Wars, in the movies anyway, is not a morally gray, nuanced world. What makes Star Wars most appealing to me is the fantasy / hero's journey elements, combined with fun and humor.
I liked K2 (Alan Tudyk is great), but for the most part I felt that Rogue One lacked characterization and humor, and ultimately it was pretty bleak. I appreciate the effort to cast a light on the "darker side" of war, which isn't really acknowledged much in the other Star Wars movies. Still, I think Rogue One is mostly missing what makes the best Star Wars movies so appealing (to me). The trouble with showing the "morally gray" parts of the Rebellion vs Empire war is that the sides are still so starkly drawn: the Rebellion is Good, the Empire is Evil.
If the main characters were better developed in Rogue One, the ending might be more meaningful to me. Why does Jyn shift from a cynical survive-at-all-costs loner to a ra-ra-Give-It-All-For-The-Rebellion! person? They don't really explain that shift very well. Does seeing a hologram of her father really change her that much, that quickly? What motivates Captain Whatshisname to give everything for the rebellion? Why are the two dudes from the temple city so willing to lay their lives down?
I was also disappointed that Ben Mendelsohn's character was so thin. They didn't give him a lot to do in the film apart from being Unhinged, Desperate, and Evil. In general, Rogue One suffers from a lack of properly characterized villains. Grand Moff Tarkin is apparently the main bad guy, and he's a difficult-to-look-at CGI rendering. Ben Mendelsohn's guy is not very smart, and not very menacing.
The lack of interesting bad guys makes the ultimate triumph of the rebels sort of lacking for me. We always knew they would get the death star plans. That they had to sacrifice a bunch of people to do it is somewhat affecting, but lacks punch because the characters were thin, as I said before. Their accomplishment was kinda weakened for me because of how uncomplicated their task was -- basically, they needed to survive long enough under fire to flip a bunch of inconveniently placed switches. Not much creative thinking involved in that one. Nobody even really had to "use the force," except for the monk dude, possibly.
None of the characters in Rogue One were as interesting to me as Adam Driver's character in Force Awakens. Conflicted, powerful but raw, not quite committed to being evil.
Rogue One was an entertaining action movie, but the story doesn't have a ton of lasting impact for me. It was a nice stop-gap between Force Awakens and the next movie, though.
I'm looking forward to seeing Mark Hamill in the next one. (That was my biggest misgiving about Force Awakens -- no Mark Hamill; that and the fact that they completely recycled the Death Star story)