Because the game is basically a return to roots, the whole series had been cleared, almost all returning to the original game. Creators have chosen to say that through a series of events that, frankly, many do not have foreseen it. Thus, the end of the last MK game, Raiden is defeated by Shao Khan, he knowing where are the rest of the gods and become the supreme leader. Raiden realizes mistakes, so he decides to send him a mental message in the past with all the events basically making an alternative timeline.
So, Raiden from the past, becomes a kind of catalyst for change if you want, getting it as small flash-backs, information to change the narrative of the first three games. Yes, MK9 is the game that everyone is waiting for. Compared with its predecessors, Story Mode really does a good job of playing a fluent narrative in which anyone, new or old in series can understand something, hard core fans reconciling to some extent.
Besides the story, you can play a Tournament mode where you can face off with one or two friends, MK9 supporting up to locally four players. The tournament is not anything to which have not met so far, considering that enables you to defeat ten opponents, three bosses, eventually receiving a part of the story in addition to story mode for every character you finished in this mode.
You can describe the gameplay from Mortal Kombat as a combination of Mortal Kombat 3 and Trilogy, implementing the best elements of both, but bringing some new ones. Compared with other fight, MK9 is a slower game, many fight based more on strategy, not quick reactions. In this game you have to learn to read your opponent, not to react to his movements, as both a game of speed of response but also a game of mind.