The Grand Prix mode is one of the two main modes of the game where you will play through a tournament as either your created player or one of the 25 fighters. (darkstation.com)
The story mode, which would be considered the main mode of the game, really doesn't contain the hook or appeal that we would come to expect from a normal story mode, but instead keeps things rather simple. (darkstation.com)
The main mode of the game is actually the World Xplorer mode, which some may find to be a bit intimidating at first, but once you see how this mode works it actually is a pretty comprehensive mode. (darkstation.com)