BioWare has confirmed a June 26 launch for release of additional endgame content for Xbox 360, PS3, and PC
Being released for free, the Extended Cut will add more cutscenes and content to the game's epilogue. According to Bioware, the additional scenes will "include deeper insight to Commander Shepard's journey based on player choices during the war against the Reapers."
Coming straight from the FAQ on BioWare's official site, "The Extended Cut expands on the endings of Mass Effect 3 through additional scenes and epilogue sequences. It provides more of the answers and closure that players have been asking for. It gives a sense of what the future holds as a result of the decisions made throughout the series. And it shows greater detail in the successes or failures based on how players achieved their endings."
After Mass Effect 3's launch, some fans were upset with the game, blaming the conclusion (by three largely similar cutscenes) did not adequately reflect player choices made over the course of the trilogy.