Metal Gear Solid V is still quite a ways away, but it looks like Gamesradar got a chance to sit down with a live (hands-off) demo of the game. Here's a culmination of everything they learned from that little session.
1. Ground Zeroes is a prologue of some kind to Metal Gear Solid V: The Phantom Pain. Kojima purpotedly stated that Ground Zeroes will function like an introduction to the mechanics of Phantom Pain.
2. Ground Zeroes takes place in Cuba, at some kind of POW camp, it seems. Here, Big Boss' first mission will be to rescue Chico and Paz from Peace Walkers.
3. Binoculars can be used to mark enemies' locations and movements on your minimap.
4. Players will be able to interrogate enemie's in order to get information such as the location of mission-vital objects.
5. Along with the famous red exclamation mark above the head, time will also slow down slightly when Snake gets spotted by an enemy. This will give the player a chance to put the guard down before he can call in reinforcements.
6. Big Boss will utilize a new google maps GPS map system. This, despite the game taking place in the 70's.
6. Driveable vehicles feature prominently in the game.
7. [Possible spoiler] It seems Snake/Big Boss is in a coma for nine years between Ground Zeroes and The Phantom Pain. As such, it seems that the "tutorial" for The Phantom Pain takes place in a hospital.
8. Cipher/Major Zero and Master Miller will be a important characters. Presumably the latter will be more important that just chatting to you on the radio.
9. Snake recieves a fancy new arm at some point in The Phantom Pain, capable of holding cigars and other complex motions.
10. FOX will face opossition in the form of XOF, a group founded to, well, oppose FOX.
11. The game will launch on next-gen and current-gen systems. How they'll manage that, though, I have no idea.
Again, you can get all this information, and more details about the demo at Gamesradar.