It should have been a riveting type film and I'm a sucker for historical dramas especially surrounding war time situations but this flick just didn't have that. Nolan has a problem with just letting a movie flow sometimes.
Was about as "riveting" a movie as you can have about a subject filled with technical arcana. He managed to make an interesting biopic that is set around multiple opaque and highly technical institutions: the U.S. Intelligence apparatus, physics departments, etc. He also managed to present those worlds and the people in them realistically, without all of the boring shadowy/mystery tropes normally used. He presented the individuals as petty, lustful, jealous, of dubious morality at times, insular, etc. All realistic.
He used music as a device to underscore the weight and time sensitivity of what was happening during that period, while still keeping the action confined to their small little world of New Mexico and university physics departments--something he is really good at. He captured well, the sense of those guys being in the own little world, as scientist/engineers often are.
He wasn't making a WWII epic.
Films like the Imitation Game didn't even come close while stuff like Good Shepherd tried to out clever itself a bit too much.
If you're comparing this to Melville's Army of Shadows, or like Bertolucci's Conformist, or that period of filmmaking. Or a PBS Frontline documentary, yea, it is lacking in substance.
But not sure what contemporary Hollywood film does it better.