Series that actually have an ending used to be rare as networks would keep them running until ratings fell below a certain level. The Fugitive (1963-1967) was one of the very first series that I remember having a definitive ending. Cable networks have changed the entire game regarding series, with creators being given greater license to tell stories the way they wish.
I was among the folks disappointed with Dexter's later seasons. And the ending copped out completely. Where Breaking Bad's protagonist ultimately paid the price, Dexter's faked his death and popped up somewhere else, raising more questions than it answered. Entourage's ending sucked as well, with everybody ending up more or less where they started.