Oppenheimer is really two movies -- one about building the atomic bomb, the other about the political fallout from building it. At three hours, it's still way too long and both the beginning and ending drag.
That middle sweet-spot is something though.
Nolan also really stumbles by using a "black and white" effect. Problem is, he uses it for both flash-backs and, very liberally, for flash-forwards. It's weird.
Cillian Murphy is great, but Robert Downey Jr. as the bad guy is really given a lot more to do which is also surprising.
It's not quite a failure, but definitely not a success either.