I love stories that do this whether they're short or novel length. The Daughter of Time by Josephine Tey is one novel which made me change my mind about an issue - in this case the innocence or otherwise of Richard III. Highly recommend the book. And To Kill a Mockingbird, when I read it at school, many moons ago, opened my eyes to racial prejudice. I hated it then, I still hate it now.
They take me out of myself and into other worlds...
When real life is grotty, sad etc, stories can act as a form of therapy, whether reading or writing them. All in all a good thing!
They produce the appropriate emotions in their readers...
I always prefer humorous stories to those that have their readership bawling away in despair. I also think it is harder to make someone laugh rather than cry. (You don't strictly need a story for the latter. Watching the news can be enough!). P.G. Wodehouse is the absolute master of humorous writing. It's always struck me to make someone laugh thanks to something you've written is a wonderful thing - clever, entertaining and a good way of increasing the cheer factor on the planet for a bit. What is there not to like about that?