That’s a really good question; I don’t think I’ve ever stopped to think about what makes a good ending for me. Having said that, I do know what frustrates me when I finish playing a game.
Did I get catharsis from playing it, or did I just hype myself up for nothing? That’s even more important if I’ve grown emotionally attached to the characters. Did the ending seem reasonable, considering the choices my character made and the context of the story? Did any of said choices have any real impact whatsoever in the ending the characters got, or would it be the same regardless of my MC’s personality?
Unless I finish the story with a “wait, that’s it?” feeling (in which case I just sit and mope, or complain about it to my sibling), I, personally, really enjoy playing the same game more than once, if only so I can see how the story would’ve panned out had the MC been bolder, flirtier, shyer, even crueller, sometimes. And, also sometimes, that only leads me to realize that the ending is standardized.
Loose plot ends aren’t necessarily bad, especially if the work is part of a sequel (I need to want to keep reading/playing, after all), but playing an entire story just to finish it with more questions than I started with can be… Annoying, I’d say. I like it when the ending makes me conscious of the choices I made, that they weren’t inconsequential, even if sometimes that means not everyone gets to be happy.