One is very odd, it would appear.
So, in no particular order, I give you some of my favorite shows (living and dead and undead) and what I think we, as writers, can learn from them.
Avatar: Begin with the end in mind
Zuko: Best character arc ever, or best character arc ever?
There is a lot to be said for saying, "We are going to create a show that is only three seasons long." They knew what they had to work with from the very beginning, and they very clearly began with the end in mind. I'm sure there were adjustments along the way (look look I know that Zuko and Katara were allegedly meant to be romantic interests in the beginning I DON'T CARE KATAANG FOREVER), but they knew where they were going and this gave them the ability to layer, and to plan, and to place details in mind-blowingly brilliant ways.
Writing a series? KNOW WHERE IT ENDS.
Sherlock: Ask the right questions
Another version of Sherlock? Did we really need that?
In this case, the answer is yes. The genius minds behind this show took the iconic character and answered a very big what-if: What if Sherlock were in modern times, an obsessive genius, possibly on the Autism spectrum, and how would his mind being so different affect his every day life and ability to function around other people?
So often the real meat of a story happens in the very seeds of the idea: the WHAT IF. If you can come up with a compelling enough WHAT IF, you don't have to worry that you are writing something that has been done before. Everything has been done before. Don't try to think of a new idea. Try to think of a new WHAT IF.
Lost: You can only ask so many questions
Oh, LOST. You started out SO AWESOME. You built and built and built the mystery, the holy crap! moments, the what-the-heck-just-happened twists! I even wrote an episode that, sadly, never aired.
And then...you didn't stop building. Every question was answered with another three questions. Threads were dropped entirely. In the end you pulled the ultimate cop-out, the "it was all a dream!" type fakery of lazy writers who lack foresight and respect for their audience.
It became very apparent a few seasons in that this show had no idea where it was going, even from the beginning episode. As a writer, do not fall into the trap of throwing in so many twists and questions that your readers never get answers. Should there be questions? Absolutely! But think of it as an exercise in trust. Answer questions along the way to show your reader that their trust in you is well-placed, and that the BIG ANSWERS you are holding until the end will be worth it.
And don't use any bleeping polar bears, for the love.
Vampire Diaries: Don't be afraid to make things happen
First, disclaimer: this is the only show on the list that is still going. (With the exception of The Legend of Korra, which is a semi-sequel series to Avatar, but it's only eight episodes in and so I'm not going to discuss it here.) And, further disclaimer: I have stopped watching it. More on that in a minute.
Plain and simple, this show works because it makes stuff happen. They resolve more massive plot points in a single season than most shows do in an entire series run. They set up the questions (or, in this case, conflicts), they let them run a mad, perfectly fulfilling course, and then they resolve them. Sure, they immediately introduce another Big Bad Plot, but as a viewer you know you aren't going to have to wait an entire season (or seasons, plural) for resolution.
Awesome! WELL DONE.
That being said, I stopped watching when one of the show writers talked in an interview about why one mass-murdered vampire would be wrong to date.
Stefan: Has killed dozens (at least). Sometimes to protect those he loves. Sometimes to protect his own best interests. And sometimes because he goes on crazy benders and just likes to rip heads off.
Damon: Has killed dozens (at least). Sometimes to protect those he loves. Most of the time to protect his own best interests. Sometimes just because he's bored.
Klaus: Has killed fewer than both of them (on screen). Most of the time to protect those he loves, though that protection is misguided. Often to protect his own best interests. Never, that I can recall, because he goes psychotic sometimes or because he is bored and doesn't have anything better to do.
OKAY SO REMIND ME WHY ARE THE FIRST TWO OKAY FOR A TEENAGER TO DATE BUT NOT THE THIRD?
That's what I thought. (Another lesson about consistency in morals, perhaps?)
Veronica Mars: Main Characters are only as good as their surroundings
I JUST WANT TO HUG ALL THE CHARACTERS, GUYS. AND MAKE THEM COME BACK ON TELEVISION.
Except maybe Duncan. He can stay in [spoiler].
So, I maintain that, while Avatar: The Last Airbender is the best series ever, the first season of Veronica Mars was the best season of any series, ever. And what the show did so well (SO WELL) was have a main character who was compelling and likable but also kind of a jerk at times, with just the right balance of tragedy and humor, and then give her surrounding characters who made her shine--both her good parts (the snark! the justice-seeking! the loyalty!) and her bad parts (the grudge-holding! the drive for revenge!). Everyone on this show played so well off each other. Even the community itself was critical and acted as the perfect foil to the action. (Another reason I [sadly] don't think the proposed FBI future jump would have worked. The show was Neptune, and her dad, and her friends. Without them, Veronica wouldn't have been Veronica.)
Make sure that your side characters are each essential, and that they each play a role. If they don't do something to or with the main character, figure out how to make them matter or cut them out. Same goes for setting. It should feel impossible for your story to take place anywhere other than where it does.
Buffy/Firefly: Let's face it
I should say something here about learning to balance tragedy and humor, or how to write amoral characters that the audience still roots for, but let's face it: You will never write like Joss Whedon. Accept it and move on.
The Avengers wish you well in your not-quite-as-awesome-as-Joss writing endeavors.
(Also, can we make a law that all movies must be written by him? Forever?)