Okay, Serenity absolutely rocks, and if you haven’t seen it, you should. Preferably after watching at least a few episodes of Firefly first. It surpassed my expectations and I felt it was a good ending to the series. That is, if it’s really an end. Part of the credits indicated that they have reserved the rights for two more movies.
Largely, Serenity felt to me like a very long episode of Firefly, although more movie-like. Unlike the series, I think there was more action than quiet crew times. Still, I loved (almost) every moment of it. The audience laughed and cried through the movie, and to me, that makes it a success.