After reading through some of the 1 star reviews, all I have to say is that some of the most common points, I see them as a bit confusing and while you aren't forced to watch this movie I think saying that the movie is bad overall is simply incorrect.
One of the most popular arguments I have seen is that "it tells the story of a massacre against the Japanese people" which I see as a massive oversimplification. The movie tells the story of an overconfident physicist looking to make a name for himself, and in doing so making a mistake, the repercussions of which he has to deal with for the rest of his life. It is not an analysis of a bomb being made, It is an analysis of a man pursuing popularity and making an impulsive decision in doing so. This movie does not tell the story of Hiroshima and Nagasaki. It tells the story of Oppenheimer, and if you end up hating Oppenheimer at the end then the film makers did a good job by making you feel something, whether you feel conflicted, angered, sympathetic or any other range of emotions as long as it makes you feel something about it then the movie succeeded.
The second argument is that "I was bored throughout the entire movie". This comes down to preference in movies, if you expected a movie about a physicist to have a scene of someone on the front lines gunning down nazi's then you came into the movie with the wrong mindset, the movie should be watched knowing that it is essentially a biography about the father of the atomic bomb adapted to a movie format.
My final thoughts are that If you go into this movie knowing that there is minimal action and it is a story of a man and not a bomb, you will enjoy it.