Pros: A little interesting in some of the displays.
Cons: Long line, displays more for kids than adults.
So you want a neat place to take the kids. This is it! You'll see mostly static displays on a guided tour about crooks who have become famous and other crime prevention work by the FBI. The kids will love seeing agents fire actual weapons on the indoor target range.
If you are much of a thinking person, you'll probably enjoy other activities more.
As mentioned by others, you'll probably wait in long lines to get inside unless you have early passes. The easiest way to get passes is to contact your congressman months in advance.
I would never rate this as a good adult experience, but it is good for the kids. It's too much of a sales job about the FBI and a little too much like an amusement park sideshow attraction. Guess you might expect that in a building named for a guy who liked to dress as a woman.
I did this tour once. It wasn't the worse thing I'd ever done, but I was glad when it was over. I'd go back again only if I had some kids who really begged to see it.