Tetris Worlds is composed of six different flavors of Tetris: square Tetris, cascade Tetris, sticky Tetris, hot-line Tetris, fusion Tetris, and plain old white-bread Tetris. By tweaking the existing rules of Tetris or adding entirely new rules, each mode requires you to come at block management and block placement with a slightly different strategy--though, for better or for worse, they're all still Tetris. Any of these modes can be played solo or against up to three other players on a single Xbox, and more importantly, you can ... play square Tetris, cascade Tetris, and standard Tetris against three opponents via Xbox Live. Square and cascade Tetris can both be played in knockout mode, where extra incomplete lines are added to the bottom of your opponents' fields when you clear multiple lines. Standard Tetris can also be played in knockout mode, as well as in race mode, where the goal is to simply clear lines and reach the next level of difficulty before your opponents. Finally, the game features a lounge mode, which takes the focus off straight competition and instead serves as a sort of chat room.