It had a short main mission, about an hour, and then a bunch of side missions on the same map like destroying anti-air emplacements, rescuing POWs, assassinating some dudes, and some other really bizarre stuff later on like... running around as Raiden shooting alien body snatchers or something.
What floored me about Ground Zeroes was how good it looked while running like a dream. I thought I'd have the usual framerate-drop choppy crap all over the place while I just suffered through it like I have with so many other games but nope.
Gameplay-wise it was pretty fun but it definitely left you wanting more which I think was the idea. Very tight unfrustrating controls.
I thought I'd include this since I didn't talk much about it before-- they've been boasting the size of their open world for quite some time now. They seem rather proud of how they've arranged the game this time.
Here's an overlay of the various games and their maps compared to the size of Phantom Pain's Afghanistan region, which is one of three of the main maps you can explore. One of the others is African jungle and I'm not sure about the third.. I've either forgotten or they haven't said anything.

If you look at Ground Zeroes' map there you can see that there may be several more camps or bases about that size throughout each region.
I enjoy exploring and finding or running into surprises. :0
Also we recently got some cross platform images comparing the graphical quality. Gotta say that PC looks the best here, not that I care a ton personally.
I'm more a fan of stability than anything else.
http://metal-gear.net/2015/08/07/mgsv-cross-platform-image-comparison/