Minecraft is a ridiculously popular game that blends exploration and creation. It would be difficult to overstate its cultural importance, particularly among young players.
Microsoft has purchased Mojang, the company that develops the game, for $2.5 billion dollars. That may sound like a lot, but it's probably well under $25 per (very) active user, which is a bargain compared to Skype or any number of famous acquisitions by Facebook or Google.
We must hope this is part of Satya Nadella's strategy of making Microsoft relevant to consumers across platforms. Under Ballmer, Microsoft suppressed their own Zune and Office apps for iOS out or fear of legitimizing any competitor to Windows. That Redmond of old also made a big gaming purchase.
Bungie was a Mac development studio that had found success with Marathon, an innovative first person shooter (you could look up!), and Myth, a tactics game. They announced their next ambitious project, Halo, on stage with Steve Jobs during a Macworld keynote.
Microsoft bought them, and Halo became an Xbox-exclusive franchise. (It was eventually ported elsewhere and Bungie spun off.)
Hundreds if not thousands of years of creative effort have been spent building Minecraft worlds. It will be best for Microsoft's brand if they respect that beyond the opportunity to "engage" users with advertising or legitimize their own platforms.