"NCIS" (the original) has been an ongoing success for 13 seasons. To gain some perspective on that, when the show started the agents were using PDAs, not smart phones. No one knew (or cared about) Kim Kardashian, Justin Beiber, Taylor Swift, Facebook (they used MySpace!!) or the Donald (Trump, not Duck.) And there was no Homeland Security.
I have to admit that I was never much interested in this show - procedurals in general left me less than enthused. I watched the various Law and Orders but not regularly (another great example of long-running episodic TV.) Netflix brought me to this show and I somehow have become hooked.
I was a "Magnum P.I." fan but not "Jag." Both were created by super-producer Donald Bellisario as was "NCIS." The show is well-crafted with great characters - a hallmark of Bellasario. You can rail against the "formula" but it works:
- Gibbs (Mark Harmon) a tough-as-nails ex-Marine who runs the joint.
- DiNozzo (Michael Weatherly) the womanizer/joker.
- Ducky (David McCallum) the quirky, yet formidable forensic coroner.
- Abby (Pauley Perrette) - a goth in goth clothing (with pigtails) who is the (also quirky) jack-of-all trades forensic scientist.
- McGee (Sean Murphy) - a whipsmart geek/agent continuously trying to figure out who he is in the scheme of the agency and his fellow agents.
- Ziva (Cote de Pablo) the hot Mossad agent who came in on Season 2 and stayed until Season 11.
Along the way they have and will rotate in other various regulars (like Lauren Holly and Joe Spano) and featured guest stars to fill in some of the blanks and create more interesting storylines and character lines.
What I admire most about this series and why I think it's lasted is that it's just damned interesting. All episodes feature four or five major elements that keep it moving at a lightning pace:
- The actual crime they're investigating. Always has something to do with the military, usually Navy or Marines.
- The autopsy of the remains where Ducky gets to give us some interesting info adds mystery (at times) and interest.
- The forensic evidence that allwos Abby to give us some cool science bits and adds mystery or solves a mystery.
- The tangential stuff (like technology, personal knowledge) that the team brings to the investigation.
- The team dynamics and how they interact with each other to solve the crime.
These elements and more are stirred into a solid hour-long drama that rarely disappoints and sometimes truly shocks and surpries.
I've binge-watched watched four and a half seasons on Netflix so far and all the crimes are pretty unique. They've had skeletons, body parts, 
modern-day corpses locked in Civil War caskets, missing persons, a corpse that wasn't dead, kidnappings that weren't, terrorist plots, smuggling, deaths in shipping containers, etc. All these scenarios involved all the elements listed above as the team works under Gibbs to put the pieces of the crime together each in their unique fashion.
Plus, the Navy and its environs (Marines are under the Department of the Navy) provide some great scenarios and set pieces like battleships, subs, and Navy bases. Also, 3-4 per season happen on or around Quantico Marine Base.
Sure, it gets a bit repetitive at times; and yes, some of the science is lame, and yes, seemingly every computer, database, and cell phone is apparently easily hackable given the story needs, but mostly it's just fun and solidly entertaining.
And it can be quite surprising in its twists and turns like the ep where the agent (torn with guilt at the death of her team) smothers a suicide bomber thereby sacrificing herelf. Did not really see that coming.
What also works is the chemistry. Casting Harmon and McCallum was a stroke of genius. They are totally convincing and their parts are well-written. Gibbs' character has depth and the right amount of sensitivity and skills. A former Marine sniper, he lives by a mancode that beats hard inside of him. He has flaws, he has ghosts (a dead wife and daughter, a past filled with death as a soldier) and he has mad skills as an investigator. Plus, although gruff mosttimes, he cares about and runs his team like a well-oiled machine getting them to work and play together while they in turn love and admirie him (meaning us - we love and admire him as well.)
Ducky is Scottish in all the right ways and quirky in all the others. He drives a vintage Morgan (look it up - it's cool,) has an elderly mother who he dotes upon, "talks" to his corpses and to anyone's ear he can grab and he's an encyclopedia of interesting trivia and hard science facts as he peels back (literally) the particulars of the victims.
DiNozzo is somewhat of a moving target; they couldn't continue to make him the hound dog, womanizer he was forever so they're currently (in 
the Season 4 I'm watching) giving him a love interest (Scottie Thompson) who I fully expect to die soon (or go away somehow) and then they'll most probably reset him but with differences since he will also have these happy but dark memories of his one, true love. Actor Michael Weatherly plays the character with dash and panache that is a joy to watch. His character's background is as a former cop so he's got skills and expertise the others don't possess.
(note: saw the eps with resolution to the DiNozzo love interest and she indeed did go away but not how I imagined.)
McGee is the constant victim of endless teasing by various team members but he's also got solid friends and terrific strengths that show up in places to change the dynamics of the storyline. For example, he turns out to be a successul novelist and is writing fiction about the team. He's also a graduate of Johns Hopkins and MIT which give him computer and science skills.
Abby, the goth-with-a-heart-of-gold is at times coquettish and sexual, and other times funky and sincere and just a great scientist who relishes her geek and freak flags. She's perhaps the most complicated character of the bunch because just a tweak one way or the other and she becomes a caricature - something that almost never happens.
Ziva can be a bit irregular but the idea of a female with her training that both serves and hurts her is wonderful. She's Mossad, Israeli special forces (Cote de Pablo is actually Chilean-American) and expands the show to a more international flair since she worked traking down bad guys all over the world before she became a team member.
Mix this with past and current players and the show seems to be endlessly variable, entertaining and solidly dramatic even it you can't call it as brilliant as say, "The Wire." But few things are, really.
The point however about the familiar formulas is that we come to these shows for the comfortable and reassuring character types and storylines. "Criminal Minds" is another show that does this well as is "Bones." But at the same time we don't want to be "talked down to." Taking your audience for granted is a surefire way to lose them. I never feel like "NCIS" marginalizes their fans. After 80+ eps I'm still looking forward to the next case, the next twisty plotline. Maybe I won't be as sanguine in Season 10 but I have a feeling I will because the show won't stop trying to entertain or amuse me in a smart and accessible manner.
I'm very late to the party for this show but I am fully invested now.
I hope it runs for another 13 seasons.
I'll probably still be watching.