on rails

on rails
 adj.— «One of the shorthand ways of criticizing a modern game is to say that part or all of the game is “on rails,” meaning that the player doesn’t have control over his or her character’s path through the level.» —“‘Zelda’ Vs. Mode Ends — N’Gai Goes ‘Manhunt,’ Stephen Changes Tune” by N’Gai Croal MTV Multiplayer Nov. 1, 2007. (source: Double-Tongued Dictionary)