Several things are necessary for a successful last chapter.
1. The most important loose ends need to be tied up. Your readers will want to know what happened to that mysterious family member, whether the villain was killed in that final fight or whether he got away, and how those fighting his forces fared. They will want to know how people are planning to go back to normal or whether they will now have a new normal – and a new normal, a new life, is infinitely more satisfying after an adventure. Nobody wants to read a book where the characters finish exactly where they started. Smaller loose ends can remain mysterious if you plan to continue the series. If you don’t, sometimes you can leave the reader to join a few dots. The main thing is, don’t leave them dissatisfied.
2. A resolution needs to be found. Even in an ongoing series, I try to find some sort of resolution for my main characters in the final chapters of my novels. Perhaps they have grown in a way that they were trying to all book. Perhaps they at last have a family or security in some way. Even if other things are looking bleak, there should still be some sort of denouement for the hero – something that leaves the reader feeling like something has been achieved… unless your goal really is to write an abject tragedy.
3. The main character needs to have grown. This especially needs to be evident in the last chapter of the book. How has the main character changed? How did answering the call to adventure affect them in the end? How are they now a better character than before? At this point, you reader should respect them and aspire to be like them… not because they started perfect, but because they had the ability to change and grow.
And this should be the most satisfying point of the book.