I had a classmate of mine at Annapolis who was placed on restriction over the Christmas holiday for a conduct violation. Over that holiday somebody came through his area of the dormitory and stole a bunch of computers. NCIS was convinced it was him so they took him out to a hotel room in the middle of nowhere, without legal representation, to question him for 12 hours. He said he sat there for 12 hours repeating the same truth over and over again.
I have met a few agents that were pretty normal people, but as an agency I have never trusted them.
The TV show may be to NCIS what the Iwo Jima photo was to the Corps. Only Iwo Jima was real.