Ms. Pac-Man Maze Madness (ミズパックマン メイズマッドネス?) is a 3D, four-directional control (block-based) puzzle game starring Ms. Pac-Man. Unlike the previous 20th Anniversary Pac-Man World, it is not a true 3D game, but uses the same format (and likely modified engine) as the mazes which could be unlocked in that game via the Galaxian doors.
PlotProfessor Pac learns that the witch, Mesmerelda, has seized control of the Enchanted Castle using black magic and from there is planning on stealing all four Gems of Virtue (Generosity; Truth; Wisdom; Courage) to control the "four wonders" (areas of Pac-Land). He creates a device called a Pactrometer which allows Ms. Pac-Man to go to these areas to recover the gems before Mesmerelda can get them first.
Source: Wikipedia, "Ms. Pac-Man Maze Madness", available under the CC-BY-SA License.