Only as brief as you allow it to be
What is essentially a playable teaser for Metal Gear Solid V: The Phantom Pain gets a ton of stuff right. It serves as a transition for experienced MGS players to the new control scheme; shows newbies to the franchise what 5 is gonna be like; and gets you unreasonably excited for the full game. The controls are close to perfect, I was using a 360 controller on the PC. It looks incredible, especially the rain-soaked main mission.
Once you play through that main story mission - probably an hour or two for most folks - the side missions that open up give you more chances to play around as Kiefer-Snake and just enjoy the best stealth action in the biz. The big complaint about GZ is its brevity, but you gotta give the side missions a chance. You're gonna get bored with the map eventually after playing through each of them, sure, but that just makes me want TPP that much more. If you're into improving your performance, though, you can replay missions with tougher difficulty. Wasn't for me, really, as the enemy AI is much less forgiving than previous MGS games.
I'm surprised I came back to this as often as I did, replaying all of the missions several times, simply because the controls and stealth action are super satisfying. If you're new to MGS, and you enjoy stuff like Splinter Cell, let this be your first taste, because for the cost it's a great value.