As series finales go, they seem to come in two variety. A finale will either be a hit or it will be a miss. When they miss, it's awful. I've seen a few of the big league finales. I saw the end of "M*A*S*H", which I think still holds the record for most watched finale. That was back in 1983. I was 19 years old. It was a great ending to a great show.
Fast forward to 2005. "Six Feet Under" is ending. That could be the best series ending of all time. Of course, that's subjective, and this is my opinion. The end sequence was a montage that used the song "Breathe Me" by Sia. I instantly fell in love with the song, so that was a two-fer. But even better than the song, was the director's choice to end it the way he did. It was masterful. Once in a while, I watch the ending just to recapture some of that feeling.
The series finale to "The Sopranos" was good, and spawned a debate that continues over 20 years later. I actually live less than a mile away from where they placed Uncle Junior's house. Yet, the end of "Breaking Bad", another amazing show, left me flat. It was clever but too tidy.
That brings us to "Billions". In a way, the ending fit the series. It was obvious but clever. No spoilers here, so you'll have to have seen the show to know whether you disagree or not. For my money, it was a very satisfying ending.