Well, the kids really don't like it so much, but for me, getting there is always a special treat. There is something about seeing a real Concorde or walking through LBJs Air Force One that is exciting or to actually touch the A-12 which goes Mach 5.
They have literally spent $100M renovating the place and now the Personal Courage Wing is not to be missed. It uses dioramas to help you get across what trench warfare might have been like. There are literally hours of video that you can look at too.
The Red Barn is the original Boeing factory and there too, for the plane nut, there are models and the history well laid out. Finally, the lectures are amazing. The WWII generation is dying out and those regular lectures are the last time for many of us to hear history in person.
As an aside, the flight camps are really great. The kids have been to two of them and it is wonderful to see them play out there on the lawn and learn about aeronautics. The older kids actually get to fly a plane and the younger ones work together in a Mission Control simulator.
This place is also wonderful for Birthday Parties. Alex has his there and it is still well remembered.