What makes an ending good?

Something I've noticed recently is how many books and movies have a great premise and strong overall story, but then fall apart at the end. I started trying to think of ways they could have been improved, but it was more difficult than I realized. I don't necessarily need it to be completely satisfying with every aspect being tied up neatly, but I can't always put my finger on what it is that could have been done differently. So what does everyone think makes an ending good?