Well crafted movie. The timeline shifts aren't that hard to keep track of if you are truly focused on the movie. This movie has political tones, and it'll definitely help if you do some background research, or slightly dip your toes into the history before watching. Look into specifically the arms race, cold war, and Los Alamos briefly. At best it'll prepare you for the movie, and won't be a spoiler.
Definitely confused why some people are voting one star saying its bland, I believe they either failed to understand the scientific relevance, do not understand the political landscape of the time, or have no context. This movie is not for such a crowd.
Best biopic I've seen to date.