Nolan's two themes throughout his works up until Dunkirk are
1) the evolution of your identity over the passing of time
2) his films collapsing under the weight of their lofty ideas in the third act
Having two, TWO, audience surrogate characters that others need to awkwardly stop and explain rules of the universe to, right down to the last half hour of the film, should have given someone pause.
Of course, similar to most of Nolan's other films from this ambitious middle-era of his career, the first 2/3rds of the movie are good enough to mostly forgive the moments where it swings and misses.