This is a pretty common criticism (and I agree with it). To me it felt like the successful test was the obvious dramatic climax of the movie, but then you had a

This is a pretty common criticism (and I agree with it). To me it felt like the successful test was the obvious dramatic climax of the movie, but then you had another hour of a bunch of guys sitting in a room arguing about security clearance. It could have been shorter, or if they wanted to keep the length they could have explored Oppenheimer's early life in more detail.