What i am particularly interested in:
the journey of the different parts for the assembly and the operational planning
the flight crews, how they felt in the moment and the days leading up to it
the Japanese decision makers, how the bombing influenced them
the people on the ground, how it effected them
the explosions themselvs, what was the detailed effect of it
The best overall book is still probably Richard Rhodes, The Making of the Atomic Bomb (1986). There are a few others since then that try to do all sides of it, but usually end up screwing up one or the other. The best books tend to focus on one aspect of it at a time. For example, Hasegawa's Racing the Enemy is very good at the diplomatic aspects of the whole thing (which includes the Soviets, the US, and the Japanese). Whereas Hersey's Hiroshima is still the most vivid and touching portrait of the effects on the ground.