The novel-style TV series
Series generally considered to have been cut short all have one common thing in common. It's that they unfold like a novel.
See, in a published book series, so long as you can get your first book published and it becomes a hit with the masses, it means that so long as subsequent books keep selling, you have the liberty to write for as long as you choose doing whatever you like with your universe. You can even make up things in between books that can give previously innocent events far more significance in hindsight. This is a sure trait of longer books series such as Harry Potter
and A Song of Ice and Fire
The problem with this style is that it assumes that it will get a continued production until the end of the story. Unfortunately, real life can have some unexpected components. Television for one does NOT work like the publishing industry, and thus finishing a story from season to season is a less certain prospect in the weekly TV setting. True, you can be assured beforehand that you'd have more time to write, but writing as if you were guaranteed a finished story when you're not is a VERY risky business.
That's why fans of a cut short series get so angry at their cancellation. Where their stories were stopped, there was still more to tell, and thus there was an overall feeling of emptiness on a show not giving closure to them.
And indeed, such a style of creation can make for very satisfying conclusions coming off of season cliffhangers or book to book cliffhangers. Works like Doctor Who
, Transformers Prime
and Harry Potter
make use of this style and the cliffhangers provided at the end of a season allows the audience to be drawn into the story even more, because the suspense between seasons has us worrying about what will happen next in the heroic quest, and its partial resolution after the break only makes us enjoy the show more.