The moon has exploded. Needless to say, that means only one thing: astronaut deathmatch! Shattered Horizon is set in the not-quite-possible near future in which humanity has been plundering the moon for its cheese, and the resulting accident ends up blasting billions of tonnes of rock into orbit. This means that thousands of space workers are trapped up in the sky, with just a broken moon and the remains of Earth's by-then-extensive space infrastructure to live on. Two factions who were feeling a bit grumpy with each other now see this as an excuse for open hostility, and fighting in zero-gravity commences.
What we have here is a first-person shooter of the well-understood competitive multiplayer genus. That said, the species itself is one of universal movement: you're free to cruise on all axes, spinning, strafing and swooping as you see fit. There is no up and down: you're in space. Shattered Horizon's clearest accomplishment is that of making that zero-gravity control system intuitive and playable. Any FPS player will adapt to it in moments, even if it does take a while to get a hang of the combat itself. Movement is immediately comprehensible, and that counts for a lot in a game in which staying alive is a difficult task.
Combat takes place around a series of space facilities, where two teams perform recognisable FPS tasks, such as capturing various points and holding them against the enemy for a set number of minutes. Respawning brings you in at a particular point in the facility, as if you'd come zooming out of space, and then you have to navigate the facilities to make your way to combat. While you're able to move in every direction in your space suit, your acceleration is limited, so it's not entirely realistic. That, at least, stops you accelerating off into the depths of space, which would otherwise be a danger. That's not to say you're entirely free of any kind of anchor, however, since you're able to use your sticky/magnetic boots to latch onto flat surfaces and walk about.
Combat is fierce and brief. Weapons do a lot of damage to fragile space suits, and headshots count. Get depressurised and you'll float away into the void, limp and dead. Melee strikes are one-hit kill, too, so if you can get up close then you're almost assured a kill. My sidekick playing with me was regularly getting lost simply by being upside-down and not knowing where he was. The game regularly feels like a test of your spatial awareness, and that's even down to mapping the momentum of enemies and being able to predict where you'll next seem them after they disappeared behind a row of floating cargo-containers.
What's interesting about suit damage is that it reduces your ability to hear. Sound, you see, is simulated. This is a nod to the reality of no-sound-in-space, and also an acceptance of the fact that no sound in FPS combat would be enormously problematic. What this means is that you can always hear your own gun and your breathing, but you can only hear enemy weapons if your suit is fully powered up.