The game contains a variety of different modes. Historical Fights is the main game mode, which pits Rocky against all of his various opponents throughout the franchise.
There are 27 different character selections possible. There are separate versions of Rocky which vary in age, weight (depending on the film) and clothes (black/gold, white/red variations). There are alternative versions of Apollo Creed and Tommy Gunn has two different selectable outfits. The player can choose from 18 different arenas to fight in, including many of the film franchises major boxing arenas, such as the Philadelphia arena and Las Vegas.
Source: Wikipedia, "Rocky Balboa (video game)", available under the CC-BY-SA License.