After thinking about the film over the last couple of days, I would probably now give it 3/5 stars. Its in no way a bad film, in fact it has some wonderful moments, but once you start thinking what works and what doesn't, it begins to lose some of its lustre, and for me it quickly became apparent, that my initial reaction was riding off of the high of that Vader scene.
Here is what I originally wrote. Basically I felt most of the problems stem from the writing. Characters and their motivations are far too underdeveloped, so when they are killed off, their deaths have little weight to them. I also didn't like how the movie ended (further explained
here and
here).
However, in addition I also realised the movie doesn't bring many new things with it. Look at the past movies and how they expanded on previous instalments.
Empire - Bespin, Hoth, AT-ATs, Lando, Dagobah, Yoda, and so on.
Jedi - AT-STs, Emperor, Jabba (and his palace), Speeder bikes, Endor, and so on.
Prequels for all their faults, had a huge swath of new characters, places, vehicles, aliens etc.
The Force Awakens, whilst often considered a bit of a retread, still gave us the first order, a bunch of new characters we were invested in, starkiller base, etc.
I feel there wasn't a great deal of cool new things in Rogue One. Though I quite liked seeing Vader's castle and Scarif.
Something I noticed, and I imagine it is the same for a lot of others, was that my favourite scene was Vader at the end, and it its a bit of an issue when you realise he is only tangentially involved in the plot.
Anyway, I am planning on seeing it again at some point, so after a second viewing I might find some of the issues I found are not so much of a problem.