"Shattered Horizon" is an unusual take on the standard "space marine" genre, in that it actually uses space in gameplay. An FPS set in zero gravity, "Shattered Horizon" puts players in the shoes of combat astronauts waging war in Earth's orbit.
The game itself is fairly simple - there are two sides, denoted by their blue or yellow spacesuits. The game itself is multiplayer only - no story mode or anything along those lines. The gameplay itself is simple, but the way it's carried out is complicated. Players have complete freedom of movement - thanks to the zero-g and their suit's thruster pack, it's possible to go up, down, forwards, backwards, or rotate.
Additionally, the player can magnetically attach to floating debris or space station parts (useful for stabilizing shots, since it's hard to aim while floating). The game uses a 3d radar that, to be honest doesn't work particularly well. The heads-up display highlights allies and enemies, but the tendency to not highlight enemies just out of range means that players shouldn't rely too heavily on their suit. Players also have the option to "go silent", turning their suit off to make themselves invisible to radar in exchange for all their own systems and thrusters being turned off.
There is, disappointingly, only one gun in the game - a standard assault rifle with a grenade launcher. The rifle performs adequately, and is also mounted with a scope for long-distance shooting (which is basically impossible if you're not stabilized on a surface). The grenade launcher has three different types of rounds - suit-disabling EMP rounds, vision-obscuring ICE rounds, and explosive MPR rounds. Finally, the rifle has a mounted bayonet that can be used to rip open enemy suits, exposing them to the vacuum and killing them instantly. Various similar realistic damage models are used - hitting the visor or tank of the enemy's spacesuit does more damage than hitting the armored body or helmet.
The graphics are decent, but kind of hard to see in parts (which is crucial when a few hits to your tank can mean your death, and when an attack can come from basically anywhere). The sound is good - switching your suit off disables all sound except for direct vibrations, which I thought was a nice realistic touch.
Ultimately, though, Shattered Horizon seems more like a tech demo than a real game. It has neat ideas and decent execution, but the limited gameplay and arsenal result in a feeling like it's not quite done yet. However, for $20 on Steam, you could do worse.