Ground Zeroes sits in a weird spot in the Metal Gear series. Not a full game by any means, it serves as an essential quasi prequel to The Phantom Pain, and for what it's worth, it is a blast, for the few hours it presents. Ground Zeroes' "story" can be completed in just under an hour, less if you've figured out the right path to speed run it. However, you'd be doing yourself a disservice to dismiss all the game had to offer if you only gave it that story mission. The base in the game is packed with easter eggs and side missions to take on. Though essentially a demo, Ground Zeroes is still a great introduction to the utter chaos that would be The Phantom Pain, and it's a must play before jumping in.