I actually picked up the Ringu Anthology when it was released. It includes all 4 Ringu movies:
Rasen- This weakest entry in the set is a direct sequel to "Ringu," and tries to weave a plot thread about a virus that infects any person who watches the cursed video. Though it adheres to some of the genre standards, the thrills are few and far between. Even for a story where a high level of suspension of disbelief is required, the plot line of a doctor trying to solve a mystery that clearly has no scientific basis just feels wrong. There are also precious few innovations of style in what comes off as little more than a perfunctory exercise.
Ringu - The granddaddy of Asian horror, or J-horror, was based on a bestselling novel by Koji Suzuki (as are all the movies in this set) and directed by Hideo Nakata, both of whom have become icons of the genre. Unlike the Americanized version, Ringu is perhaps more nerve wracking for the psychological tension it develops in the mystery of a cursed videotape, Sadako, the tormented girl dead for 30 years at the bottom of a well, and a little boy and his mother who must unravel the secret before the curse catches up with them. The details of life in modern Japan become all the more sinister as routine is upended by unfathomable madness.
Ringu 2 - Back in style, form, and disturbing content, this more apt sequel again finds director Hideo Nakata at the reigns (as he was for the much different take of Hollywood's The Ring Two). The story follows the young research assistant of Ryuji, one of Sadako's victims from the first film, as she becomes involved in the mystery of the tape. Ringu 2 intriguingly expands on the themes of the original film while resurrecting some of its characters and introducing new terrors. It also expands the stylistic limits of how horror movies can be all the more effective for stressing subtlety, intelligence, and uniqueness of vision.
Ringu 0 - Perhaps the most absorbing of the four, this prequel to the Ringu saga takes place 30 years in the past. It reveals the origin of Sadako's miserable journey to becoming a hateful spirit seething with wrath, rotting at the bottom of an old well waiting to reap vengeance on those who cast their gaze in the wrong direction. Full of inventive visual flair, there are some seriously creepy moments and ingenious sequences in the story of an acting troupe whose members mysteriously vanish or go insane. Sadako may or may not be behind it all, but the bloody finale makes clear that she'll have her revenge, whether she is to blame or not.
And if you love watching Ringu, this is the set that is a must own. No doubt about it. The full title for it is called Ringu: Anthology of Terror. Trust me. Go buy this and it has 4 discs to it. This was also released back in 2002 and runs somewhere between $35-$40.