I'm actually nearing the end of my story's first arc and for a while, almost 10 chapters or so in the middle of it, I wondered how and where I would even wrap it up. I know the overall end of my story and have some events planned, but my current arc wasn't something I had actually thoroughly planned... It actually exploded on me and now I have this... thing that weighs heavily on my MC. Is it a bad thing? No. But it happened and now I'm dealing with it.
The ending to this arc actually came as a random idea that I fleshed out, talked with friends and acquaintances over, and actually put the most thought into when I was drunk. Now it's closing up very neatly. There is a lot more I would like to add, more things I want to do, more blood to be shed, and honestly; looking from the end backwards I see much more that I could have added in terms of character growth. Things just seemed so... fast. But, it's a natural ending. It's coming to the finale at just the right time and the crescendo is working just the way I, the maestro, need it.
It may leave a sour taste in some reader's mouths, the way I end it, but the show must go on and this train does not go gently into that good night. I have made that clear with events before so they better be ready for it. As I always aim with my individual chapters; so long as the arc ends in a concise and understandable manner, then I am satisfied with it. Regardless of the ending that happens.
That also goes for any story I read. The ending doesn't need to be powerful. It doesn't have to be some grandoise, explosive rattling of emotion that brings tears to my eyes or makes me leap with joy after the Hero achieves victory. No. It can be a solemn, quiet ending. One where the characters come to peace. A quiet whisper where, after some trials, the couple just sits down and smiles warmly with one another over a cup of coffee and is now looking forward to a joy filled life ahead of them. Maybe an adventurer finally decides to call it quits and finds himself sitting down at a bar he loves with a pretty waitress serving him a beer, causing him to decide to marry her and have a family.
So long as the ending brings the story to a conclusion and the individuals involved have an end with closure that is both believable and matching of their characteristics, I am satisfied as the reader.
The story ends when the plot is complete. The goal the MC set out to achieve has been achieved, the big bad boss is dead and the world is saved, or the harem is established and the MC is now forking them regularly like some rabbit with an aphrodisiac. But, the ending doesn't need fireworks.