Of course, if all goes wrong, it's entirely possible to "go loud," so to speak. If you're spotted by a guard, you're given a brief window to dispatch them quietly in which time slows down. Fail this, and the alarms sound, and you must choose between fighting, running and hiding. Ground Zeroes' combat takes its cues from any third-person cover shooter of the last seven years, and so is perfectly serviceable in this regard. But it's undoubtedly a stealth game at heart, and that is a Very Good Thing.
Ground Zeroes' story is a brief affair, but it isn't the end of the game. Alongside it are five additional missions, all set in Camp Omega but with different objectives, different entry points, and different times of day. Unfortunately, they're a mixed bag. Some, such as assassinating two particular marines or making contact with a double-agent, are excellent emergent sandboxes, as you try to locate your target, using photographs in your inventory to recognise them, before completing your objectives and attempting extraction. But then there are more action-oriented missions which force you into a particular role, and simply aren't as interesting.
Ground Zeroes has other issues too. It commits the cardinal sin of doing something in a cut-scene that would be more fun to play. After a mission there's a scene that involves an extended fight on an oil rig (before you squeal "spoilers!" it was in the trailer, so shush). Given that all the assets for that scene had to be created, it's daft that Ground Zeroes doesn't involve the player in this, especially when you consider it would pretty much put to bed cries of Ground Zeroes being "too short".
Regarding this, it's a daft complaint. Ground Zeroes is as long as you make it, and is more about experimentation and exploration than it is about "getting to the end." That said, referring to the story mission specifically, it doesn't entirely escape that feeling of being an introduction to something else, rather than a work in its own right. The ending is too abrupt, and our time with the characters insufficient to fully get a handle on them. As for whether Ground Zeroes' content justifies the price-tag. It's definitely worth playing. Whether it's worth £30 to play right now when there are so many other excellent games like South Park and Titanfall and Dark Souls II out in the wild, well, that's entirely down to you.
There is one other thing we need to mention that might sway you. Ground Zeroes is a game with something to say. Its Camp Omega is very obviously based on the US Camp X-Ray at Guantanamo Bay. In fact, despite being set forty years in the past, for all intents and purposes it IS Camp X-Ray, again highlighting the attention-to-detail evident in so much of Ground Zeroes' production. It's unflinching in its depiction of the dehumanising brutality with which its prisoners are treated. Kept in cages in one corner of the camp, they sit prostrate, manacled, with black bags over their heads. They're denied not just the rights of the legal systems the developed world claims to uphold, but the right to move, the right to see. And that's merely what's obvious in the most cursory of playthroughs. Look a little deeper, explore the camp and the experiment with the game's systems, and you'll discover far worse goings on.
Into this Ground Zeroes drops you, and asks you to rescue just two of the dozens of prisoners kept inside Camp Omega. The Internet has already proved it is possible to do this and head home for tea and celebratory cigars within ten minutes. But when you leave those cages behind, with the other prisoners begging you, desperately, to help them, there doesn't seem much cause for celebrating efficiency.