There is one thing that games can do and that no other form of media can. And that is allowing the players action to have consequences in the game we are playing. Books, movies, music and all other form of media is very passive. We are just spectators there. In games, on the other hand, we can interact. We can affect the events around us.
Except, very few games are like that. Usually is you going from point A to B, killing stuff, pushing levers, solving puzzles, etc. In most game, if you left one enemy alive or don't get a certain item, it have no effect further on the game. Your actions have no consequences.
Other games, like inFamous or Bioshock, give the players the ability to change the outcome of the game. But it is usually very basic, like 'save the burning orphanage' vs 'throw a kitten in the fire because it is fun' kind of choices. Also, the after effects of your choices are rarely felt, usually just changing the very final cutscenes.
And that is a missed opportunity. Games, like no other media, can show the consequences of certain actions, show the player that no action is without consequences. Games can be a powerful tool to generate critical thinking, because it can make the player think of their actions.
But due to the technical difficulty involved in creating such a system, most developers rarely explore this as it can be. Others use this traditional black-and-white dichotomy of good and evil because it is easier. Others, probably afraid of stepping in mine fields, avoid it.
Games can create a revolution is how stories are told, in how messages are spread. All it needs to this to happen is someone clever enough to use the tools at his disposition.