At the end of the original Black Ops, you got a special bonus game of zombies where you could play as President Kennedy, President Nixon, and Fidel Castro. After the credits in Black Ops II, you get this.
Obviously major spoilers here, but for those of you that don't care, you get to witness Avenged Sevenfold perform "Carry On" with the help of Frank Woods on drums and main villain Raul Menendez on guitar. In the audience are largely all the characters you meet in the game, including the President shaking her booty.
I spoke with Treyarch not too long ago and found out that Avenged Sevenfold are huge fans of Black Ops. The band takes the game on tour with them, and sometimes the concerts are delayed because they may or may not be too busy playing the game. Videogames!