I would count this museum as a must see because of the importance of atomic weapons. It is good. But I also would say it's about half what it could be. I mean that positively: there is so much historical context that would be interesting, about the bombs that ended World War II, the decision to use them, the Manhattan Project that developed them, and so on. The former Soviet Union and other nuclear powers also could be discussed.
My suggestion is not quite fair though. This institution is much more focused. It's about the testing of the weapons. So it has great material in Native Americans and their history on the land, as well as the environment.
I tend to go through museums too quickly. Still, I doubt you'd spend more than an hour here.
Let me be clear: I enjoyed it, and I recommend it without hesitation. It is the beginning of inquiry, not the end, and that is the purpose that a museum is intended to fulfill, to spark interest.