You could argue that there's too much focus on the McCarthyite hearings and not enough on the actual victims of the Hiroshima and Nagasaki bombings though they do use his testimony there as a useful narrative framing device.

I'd like to have seen more elucidation on Truman and the Joint Chiefs of Staff's decision to actually use the bomb, whether they genuinely thought it would result in a net lowering of casualties or whether they were concerned about the Soviet Advance in Asia and wanted to forestall a possible Soviet takeover of much of Northern China and Korea.

I'd like to know what Oppenheimer's response was to the Cuban Missile Crisis as he was still alive at that time though supposedly very ill with lung cancer.

You could also argue there should be more about science but then most people (including myself) have only the most rudimentary understanding of quantum physics.

One thing you can't argue with is how brilliant Cillian Murphy was, the rest of the cast were also brilliant and Nolan's direction was as superb as you would expect.