English Title: .hackOne of the early successess of the "episodic game" concept, built around the concept of a mysterious and possibly-malevolent MMO game-within-a-game called The World. The story follows a small band of players looking for answers as to why other players are mysteriously falling ill while playing the game. Supposedly rather mediocre as an actual game, but elevated by the (at the time) unique and surprising story.
Japanese Title: ドットハック
Genre: Episodic RPG
Released: Jun. 20, 2002 / Sep. 19, 2002 / Dec. 12, 2002 / Apr. 10, 2003
Product Codes: SLPS-25121 / SLPS-25143 / SLPS-25158 / SLPS-25202
JAN 4543112084477 / 4543112084484 / 4543112084491 / 4543112084507
I haven't played these yet, but I'm particularly fond of the character artwork provided by Gainax's Yoshiyuki Sadamoto (Evangelion, FLCL). Each game includes a supplemental anime DVD, and the box set also includes an utterly strange bonus DVD called .hack//GIFT, which is a parody anime done entirely in a goofy chibi style. The box and bonus DVD were given out to people who purchased all four games at launch.