When Should a Series Die?

People love a good series.  They get to know a set of characters, a certain city or world, the types of conflict or subject matter to be expected, etc.  It can feel like coming to visit with old friends.

But when should a series end?

Should a series ride the wave until no one is interested anymore?  Should it end where people clamor for another installment, even if it never comes?

I hate shows that end a season on a cliff-hanger if it isn't already renewed.  Why?  Because there is no guarantee of resolution.  Even if it doesn't tie every loose end into a pretty bow, the immediate arc should play out.  

Books are the same for me.  Let me know the characters live on, as I do, but don't leave them in a soap opera fade-out.  I just like knowing.

And, with incredibly few exceptions, spin-offs annoy me.  Don't assume I'll follow another set of characters through your wilderness unless there's interest.  

Chalk me up as one gal who likes a softly closed door, a setting sun, and a natural ending.

What's your least favorite way to end a series?  Which series (books, movies, shows) have done it best?