Completing the first mission unlocks several more. There's a decent amount of content in there and it's not an expensive game. I love the mechanics, though, so I had no complaints for $10 or $20 or whatever I paid for it. MGSV has an insane amount of content in comparison of course. GZ is very much a prologue.
Havent been able to touch MGSV in a few days. Too busy. I'm pining
I did see the content after I finished the main mission. I might look into it at some point, but I'm set on MGSV now.
I really liked the additions of the cameras and spotlights to make it a little more difficult to go through. Definitely more complicated than MGS3.