Lost and Fringe Come to Mind
I agree with you about the nature of story. The show that comes to mind is Lost. They decided to tell dozens of small stories but they only had one way to resolve anything: death. So they killed people off and brought in new groups of characters to replace them (the Others, the Tailies) but this meant so many questions in need of answers that the disappointing finale was inevitable. (BTW, I think Lost owes a big debt to "And Then There Were None" by Agatha Christie).
Fringe had a novel if not entirely successful approach to keeping it fresh. They changed the premise of the show 3 times. When it started it was a straight X-files clone. Then it became a sci-fi show about parallel universes. The final season took place 25 years in the future and involved overcoming an invasion by future humans with mind powers. I stuck with it but their ratings dropped each year, partly because the back-story became so convoluted. The successfully landed the final season but only because they only had 13 episodes built on a fresh premise.