Ending A Beloved Series (a Semi-Rant)

I know that it is all up to the authors how they want to end a series, but I also know this, there should be some reward for loyal readers who have stuck by a series till the end.

I have a couple of girls at my school who read Divergent and Insurgent for the second time this fall in preparation for Allegiant.  They wore black to school on the day it came out (for Dauntless).  They squealed when I handed them shiny new copies to check out.  They smiled and read through lunch.  They were SO excited.

Now, they stand at my desk in the morning and warn everyone away from even starting the series.

I know what happens even though I haven't read Allegiant (mostly because the aforementioned girls told me, but I also saw a lot around the blogosphere shortly after the book came out), and I do have to wonder why the author did what she did.

Like I said, I didn't read it so I don't know all the details around what happens but was there hope?  I feel a dystopian series should end with hope.

I also recently finished Jonathan Maberry's Rot & Ruin series and I have to say that it was an awesome ending to the series.  There were deaths, yes, but the series ended with hope and it was a reward to loyal readers.  I didn't feel I had wasted four years of my lives on these books. 

I don't think anyone wants to reach the end of a beloved series by throwing the book across the room and screaming obscenities.  They certainly don't want to feel that they wasted time!

Have you ever had a series end horribly (in your opinion)?  So horribly that you wished you hadn't read it in the first place?  Tell me about it!