How I Use It
I had students work off of the same account (you can have different accounts working simultaneously but I had minimal tablets in my room so it was just easier to have kids all log in on one account). Each student contributes to the world and built things, I left it completely open-ended. We then did group discussions and writing assignments around what they built and informative pieces on helping other students to build more things and become more proficient in the game. Students also wrote back and forth to each other about the world, they would critique another student for changing something in the world, or inform them of future plans they could help build. Creating the social aspect in the real world outside the game pushed vocab, interaction, and writing skills. When used in this controlled and academic focused way the game was great. That being said some kids who are proficient in Minecraft were pretty angry/disenchanted that they didn't get to fight creepers and such, but as long as you frame everything from the beginning and layout the unit goals and expectations, you should be fine. I also had students replicate great works of architecture or make their own monoliths/monuments and tell the story behind them.
Minecraft has a lot of potential and is amazing as far as video games go. You as a teacher need to have a deep understanding of the game, which is why I say set up is more than 15 minutes, you should play it for a good hour or two before deciding to hand it over to students. As an example, you'll want to go with "creative" mode or turn difficulty to "peaceful" so that student don't get caught up fighting mobs and "creepers". If you focus on building things, the social aspect of the game, and add in some educational goals, it can be a great experience.