The gameplay of Jr. Pac-Man is similar to that of its predecessors with a few differences. The maze is now two times the width of the display, and a virtual camera pans left and right along the maze to follow Jr. Pac-Man, sometimes resulting in the ghosts being off-screen. A total of seven mazes appear throughout the game, and unlike previous Pac-Man games, none of the mazes have tunnels that wrap around from one side of the screen to the other. Most mazes have six energizers instead of four. Like Pac-Man and Ms. Pac-Man, Jr. Pac-Man has a kill screen; when the 146th screen is reached, the maze is invisible and there are no dots to eat, effectively preventing the player from completing the level.
As in prior games, bonus prizes appear in each level. These prizes were called keys and fruits in Pac-Man, but none of the prizes in this game are fruits. Prizes appear in the middle of the maze, and similar to Ms. Pac-Man, bounce around for a time, but as a prize encounters dots, it changes them into larger dots that slow Jr. Pac-Man down more than regular dots but are worth more points. If not eaten beforehand, a prize self-destructs when it encounters an energizer (also known as a power pellet) and destroys them both.
There are also a few cosmetic differences: The main character is Jr. Pac-Man (who wears an animated propeller beanie); Clyde, the orange ghost, is now called Tim; and the game's graphics and sound have been updated, including a lower-case anti-aliased font for scores and game text. The game's intermissions center around the developing relationship between Jr. Pac-Man and Yum-Yum (apparently the daughter of Blinky).
Source: Wikipedia, "http://en.wikipedia.org/wiki/Jr._Pac-Man," available under the CC-BY-SA License.