Vantaggi
The mission of the NIH and do work on the projects that no one else has the resources to accomplish. The NIH is generally not affected by lack of equipment or proper tools. Its not like the university where you have to try to do the research you want with the tools you can get. Here you can use the right tool for the job. The NIH also has special access to the library of medicine with a huge library support staff. Almost all articles are online and if they are not, a librarian can scan them in for you and email them to you as a PDF.
Svantaggi
The NIH, like any government organization can quickly become an unwieldly beuarcracy. The NIH has a lot of varianace between labs and sections, so its important to get feedback specific for the lab/branch/section you will be working in. Funding comes in waves and it is hard to work your way up if you are not a MD or a PHD. Also, since its a lot like a hospital, the MDs appear to hold more power over the PHDs.