Series 3 of NCIS is where the program really blossoms. The denouement of the Ari storyline is superb, and the subsequent addition of Ziva David takes the dynamics of the team to a new level. The loss of Kate is treated in a way both touching and very funny (I know that sounds odd, but it's true), and the melding of the team as they deal with a variety of cases is a pleasure to watch.
The scriptwriting in this series reaches new heights as well. Though many of the plots contain gaping holes, the stories are carried off with such pace and verve that the viewer rarely stops to question them. The stories themselves are varied and exciting; I often found myself concerned for the fate of cast members that I knew very well - by the nature of series - would survive.
But it is the strength of the characterisation that raises this series head and shoulders above all the other police procedurals: Mark Harmon's tough but caring ex-Marine is thoroughly believable; Michael Weatherly manages to make you like the obnoxious but somehow charming Tony DiNozzo; Cote de Pablo makes the spiky, aggressive Mossad agent Ziva a wonderful counter to DiNozzo's insouciance, while occasionally revealing a gentler, vulnerable side; and Sean Murray's clever but gawky Timothy McGee completes a classic mixture that compares well with any fictional team one could name.
Neither do the supporting cast disappoint; both Abby (Pauley Perrette) and Ducky (David McCallum) have major parts to play during the series, and do it magnificently, and the smaller recurring roles are all well acted.
All in all, this is one of the best series of (to my mind) the best police series ever to come out of the USA.