Decent, solid addition...

Rating: 9/10 (5 January 2017)

...not a total work of art, true, but fits well between Episodes III and IV. I enjoyed that it shows the post-Republic galaxy where the opulence has decayed and the stakes have increased. It also carries on the original theme of Rebels challenging a tyrannical Empire, in what seems to be a grittier way than previously seen. The characters do get some development time, a nice change from previous installments where all we know is a name and profession (heck, it took 45 minutes to meet Han Solo in A New Hope, all while NOT knowing Luke's last name?!?!). There are the occasional hiccups in plot, moments where characters seem to care more than they should about each other, too early in the story but I blame that on late extensive reshoots and plot changes. Grand Moff Tarkin was a vast achievement, I was impressed because I could believe it was him (99% of the time). That tech has made huge strides since Jeff Bridges in Tron: Legacy. I do think the side plot? main plot with Saw Gerrera could have been tightened somehow, but it still held my interest.
The Great: Casting, in my opinion, was brilliant. Felicity Jones and Diego Luna made you believe in the Empire-occupied dismal reality their charascters inhabit. The supporting cast, including Alan Tudyk, were also A+. Ben Mendelsohn, you the man, as far as villains go! The plot also fit in seamlessly with A New Hope, much more smoothly than Episodes I-III do with Episodes IV-VI. CGI was nice, tight and special effects in keeping (mostly) with those seen in the older trilogies.
The Good: settings, costumes, and musical score were quite good. Like I said, the opulence of the previous era is gone, people wear utility clothing that fit in with A New Hope. I was so happy to see the return of real clothes. The score IS good for a guy who had only six weeks to do it in, not quite John Williams but close enough while still being unique.
The Not-so-good: (SPOILERS) CGI Princess Leia was not as good as Tarkin, but this clip is so short it really is easy to ignore. The odd squid-mind reading creature of Saw Gerrera's is not really needed, a modified Imperial round torture probe would have been scarier (that needle on the end, woooah!). Vader. I think he had more plot before reshoots (trailers hinted at it) but really only needed to be at the very end. Scaring everyone in the theater with that hallway appearance. Speaking of the end...
It works for me, although I felt awful (SPOILERS) about Jyn and Cassian and their ship that never sailed. It was so close, too! But I felt Rogue One gave A New Hope greater urgency, that the stakes were even higher now because the Rebellion had lost so many lives.
So my advice is go see it. Form your own opinion. See how Leia got those plans, and maybe if you rewatch A New Hope, you will see in the opening crawl their efforts come to life as you remember this newest Star Wars story.