Ring O Birthday is a great prequel to the Ring series although the director is not Nakata it is a good drawback to the previously made movies. The movie includes the origin of the mysterious girl that is Sadako. If you watched the previous Ring movies this is a source of all the confusion and questions that are embedded in the movies mentioned. Unlike the Ringu and Ring 2 this has a slower pace even though the movie was short it felt long because of the pacing. It was not scary as the others compare but this is a different genre you're looking at. Ring 0 is a good movie with tremendous writing prowess shown. The cast was smooth and the directing is not sub-par to the other Ring movies which are considered one of its kind in the genre.