I am the latter type of writer and reader, I need something to temper the fantasy bliss, to remind me that even make believe characters must work hard at happiness. (The only tale I ever gave a pass for "Riding into the Sunset" was The Princess Bride by Goldman. )
There can be degrees of trade-off for happiness, too, for example in the Lord of the Rings Trilogy, in the end Frodo has to go with the elves to the Undying Lands, but the trade-off was that he saved their world! Now, no one said the Undying Lands were bad, but he did have to leave all that he loved behind. A sacrifice, if you will, for the greater good. Give me a little Machiavelli, I guess.
But why would I or anyone want a tale like this, or conversely, want one with the perfect ending?
Perhaps, in my case, it gives characters that don't end up with happiness handed to them a depth of being...morality, justice, honour, you name it, and for each one of us it may be different.
What is your take on it? What kind of ending writer are you and why? Look back over all you've written and see if there is a pattern there, if there is a mix even of the two. Can seeing that style of writing help you?