Sword Art Online The Movie: Ordinal Scale follows the anime series with a new augmented reality game. There is a new conspiracy involved. Although the movie starts with a very brief summary of what happened before, I think it’s best to have watched at least the first season to fully enjoy this movie.
Whereas previous monster battle animated movies are significantly flawed in some ways, such as Gantz: O or the recent Final Fantasy movies, this movie presents a perfect balance of everything and shows the correct way of doing it. It recaptures the essence of what made the first season so great. To nitpick the movie, the primary flaw is that what happened in the climax, and the plan of the villain, do not make complete sense.
P.S. There is an extra scene after the credits.