What's in your view the difference between an open ending and no ending actually? Just wondering

Lately I've been appreciating open endings more and more, sometimes you can get so fed up with a forced happy ending, especially if that's paired with forced romance in stories xD. I do like happy endings sometimes, but at the moment I'm more into open endings, but... too open is also frustrating

I don't know if any of you are familiar with books from Preston & Child? Those usually end up in some bizarre open ending, which just leaves you with nothing. That can be quite frustrating, though it is fortunately often not too cliché.
So in short: more of an open ending for me, unless it's toooooo open