My husband and I devoted a whole day to this museum, and could have happily spent longer. It is a national treasure. The gem and mineral exhibit is wonderful (especially for rockhound/jeweler types like me), and my husband (interested in anthropology and archaeology) really enjoyed the human origins exhibit. Wildlife, fossils, dinosaurs, the oceans, ancient egypt, etc. -- all are presented informatively. I recommend buying a copy of the goSmithsonian Visitors Guide ($2) which is published seasonally and covers ALL the Smithsonian Museums.
This review is the subjective opinion of a TripAdvisor member and not of TripAdvisor LLC.