Didn't seem too long to me at all. Not sure why everybody wants everything so rushed and edited down these days.
It is a bit disturbing and harsh at times to say the least, but also quite powerful and moving all the same. It worked well. I suppose for once, maybe, at least in part, the ugliness and violence and disturbing stuff might perhaps be justified to be shown this time, just to truly get across the overall feeling of the horror of U.S.S.R./Stalin and more directly the true level of what the character had to face and some elements of her nature. Otherwise perhaps some of it, especially on the broader scale, but even on her own personal scale, might not really, fully sink in to people.
Also seems a bit all too relevant again with Putin seeming hell bent on going all full on 1980s level Cold War again (heck there are even some rumors that his Institute, perhaps some sort of 'Americans' and spy finishing school of sorts among other things, has expanded to include a clone of the old State School #4
and it's Swallows which I think was ended in the early 80s perhaps, although many say it can be safer and cheaper to just hire on modern trained escorts in Russia today who are sophisticated enough these days and know nothing and can't really be turned since they have no connection to anything).
One thing for people to note, is that Rotten Tomatoes can be an odd thing to glance at. You could have 99% of reviewers think a movie is a B- or B and it will be 99% fresh and seem like one of the greatest films of all time or get 60% thinking something is an A or A+ and 15% thinking something is a B+ and 25% thinking it is a C or worse and the movie will get a 75% which might seem much worse than the film that got a 99% but that would seem a bit misleading.
Anyway in this case it seemed to be polarizing and get a lot of 8-10s and then a lot of 1-2s and so get like a 50% and yet it is not that most people thought it was middling.
I also saw try to take a Millenial feminist bent on it and I feel entirely misread the movie. Just because something shows a number of characters behaving in very misogynistic ways doesn't mean the movie itself is misogynistic or celebrating any of that. And some seemed to not realize just how fierce Stalin and what the U.S.S.R. could do were. And then trash it to bits. It seemed those types of reviews played a big part in the scores that brought the overall total down.
Some just became too unsettled by some of the disturbing stuff to be able to appreciate it all and it was quite good (oddly though some of the same reviewers somehow had no problem getting through Dragon Tattoo which seemed worse and with less need for all that stuff).