Pros
Critical scientific and public health mission, job flexibility is okay (but depends upon your supervisor)
Cons
My comments pertain to the non-laboratory environment at the NIH. I have been at the NIH for more than 20 years. NIH has an incredibly important mission for the country and world, and is a great place for some people - but if you want to last here, and not become incredibly discouraged and jaded, that mission has to be enough for you. Good bosses are almost nonexistent (I've never had one in 20 years - but I've had some nightmarish ones), and NIH leadership doesn't care a whit about true leadership. Only very rarely are bad apples fired, and NIH was embarrassingly late to the game in terms of cracking down on harassment and improving diversity (women, minorities, etc.). People, especially yes-women in their 30s, are HIGHLY valued and groomed for very high level positions (that they're not nearly qualified for). White men are also valued. At the same time, there are many hardworking women over 50 who are invisible. GS-15s are expected to die on the vine... So, if you have a PhD and are thinking about a career outside of the lab, think very carefully before going to the NIH - unless having a series of terrible bosses and pay that will top out long before you retire isn't going to bother you.