Pros
NIH is probably THE best place in the government to work. While it is not without its problems here and there, NIH leadership tries very hard to protect work schedule flexibilities for all staff, they take employee experience results very seriously, and they really try to embody innovation in all parts of the organization. Overall, it is a great place and I don't know how I will ever go elsewhere.
Cons
There are a few organizations that really suck to work with in NIH. DPSAC, which handles background investigations is just horrible. They are a black hole for information so when you are onboarding you will probably be quite confused as to what is going on. The people you can get on the phone are really rude and unhelpful. There are a few small pockets like this here and there but not many.