@Slaine Your right nut is safe, I would sell a lung to play this game! 100% day one purchase for me!
Oh, and to clear up the above naming questions folks...
This was another classic Hideo Kojima rope-a-dope. All initial marketing of MGS5 was split into two campaigns to make everyone think there were two games, with various trailers for both 'Ground Zeros' and 'The Phantom Pain'. Ground Zeros was revealed as an MGS game, The Phantom Pain wasn't initially, but contained MGS characters and had a very MGS feel to it.
Hideo Kojima later revealed it was in fact one game. 'Metal Gear Solid 5: The Phantom Pain' with Ground Zeros being one of the in game missions.