The game is played from the cockpit of a mech, where the player controls it in the first person and shoots at enemy robots. There is both a campaign and multiplayer mode. The player can select from seven different mech chassis, and customize them with different reactors, shields, weapons, and secondary weapons.
In Shattered Steel the mechs of the world are known as Planet Runners, and they are almost always used primarily by mercenaries. These mechs are known for their versatility and capability of effectively being one-man armies.
In the single player campaign, the player is hired to help humanity hold off sudden alien invasions on several planets. The identity, intentions, and origin of the aliens is initially unknown. Proceeding forward, the player and human scientists learn more about the aliens, such as what they use human prisoners for, the nature of their supply lines, and how they move across planets so quickly.
Initially, the player is advised by the male AI AINIC III. This role is shifted to the female AI AINIC IV relatively early in the campaign. It is notable that the humans keep using AINIC systems, despite their apparent tendencies to go mad or homicidal. Previous AINIC models have apparently been known to turn on those they were assisting and make open attempts to kill them. Suffice to say, the only major similarities between AINICs III and IV is that they both assure the player of their loyalty upon their introduction and at least vaguely express varying levels of concern for the player's metabolism.
Lasers: One of the more common types of weaponry in the game. Lasers come in three variants, Light, Combat, and Heavy. Each higher level has progressively higher damage output, but lower recharge rate.
Chain Guns: Faster firing and more accurate than lasers in some situations, Chain Guns come in three variants, 30mm, 50mm, and 70mm. They all have higher damage output than the lasers of comparative level, but they don't recharge like lasers do. The amount of ammo chain guns start with is the same for each variant.
Plasma Guns: Plasma guns are slower firing and have slower projectiles than lasers, but hit much harder than both lasers and chain guns. However, they are also much heavier to equip and have lengthy recharge times. So lengthy, that most planet runners will want to upgrade their reactors to compensate, effectively further increasing the weight plasma guns require to be used effectively. Plasma guns come in two variants: light and heavy.
Light Missiles: The most basic and lightest secondary weapon available. Light Missiles are best used against light ground targets. They come in packs of 18 or 64 missiles.
Heavy Missiles: Very similar to Light Missiles, except they hit slightly harder, making them capable of taking on medium ground targets like Basilisks and Talons. However, their ammo counts are much lower than that of light missiles and they never get rapid fire capabilities like the 64-pack of Light Missiles does.
Seeker Missiles: In terms of damage output, Seeker Missiles are roughly between Light and Heavy Missiles. Their main boon is that they have homing capabilities, greatly increasing their accuracy and ease of use. Use them sparingly though, because they only come with 10 per pack.
Nukes: The most devastating weapon in the game and one of the prime showcases of the game's degradable terrain. Nukes will pretty much one-hit kill anything they hit with their blast radius, often including the user, regardless of how well-powered their shields are. They leave an absolutely massive flaming crater in their wake.
Rapid Fire: The only type of secondary weapon that can be recharged just like lasers. Rapid Fires are basically laser weapons, but with a higher rate of fire and slightly faster projectile speed. Their damage output isn't as high as most lasers though, due to them only firing one projectile instead of two or four. Rapid Fires come in light and heavy variants.
Flamethrowers: A specialized type of weapon that fires short-ranged fireballs. These fireballs do decent damage if they connect with an enemy, but also set the ground ablaze, further increasing their potential damage output. They can also be used as a temporary area-denial tool. However, flamethrower ammo is very limited, encouraging less liberal usage.
Mortars: The longest-ranged weapon in the game, if you can aim it. Mortars have a very high firing arc, making them ideal for harassing enemies you know are outside your draw distance. Given the slow projectile speed of mortars though, whatever you target with them had better be quite slow or single-minded in his movement direction, otherwise you'll likely never hit. It goes to be noted that the Multiplayer bots can be surprisingly mean with this weapon.
Howitzers: Direct fire weapons with high damage output. Their ammo is limited though, so make your shots with these weapons count.
Mines: Self-explanatory area-denial weapon. Mines are fired at a very short-ranged arc in front of the planet runner using them. While the mines have a very low profile and small hit box, it is possible for other planet runners to notice them on their radar, allowing them to fire upon them to destroy them from a distance.
Nova Cannon: The most powerful rechargable secondary weapon available. The Nova Cannon has a very limited max ammo capacity and slow recharge rate (Unless you come with a level 3 reactor), but it makes up for it with sheer power. Any enemy caught by the particles of its star-like projectile will pretty much be killed in one hit. It is possible to take cover from the Nova Cannon though, for it is one of the few weapons in the game that has absolutely no effect on the terrain. As such, the Nova cannon can effectively be seen as a rechargable, less destructive and lower range version of the nuke.
The single player campaign of Shattered Steel is 32 missions long and spread out across two planets. The player goes through this missions in a linear fashion, with occasional branching paths offering additional missions that can give the player certain weapons and mech types early.
Along with the single player campaign, Shattered Steel offered a co-op mode for said campaign and a deathmatch mode for multiplayer.
The cooperative mode allowed players to play through the campaign together, or turn it into a competitive mode with team play enabled. Players that chose to be on an evil team spawned on the side of the aliens and were given the opportunity to prevent the good team from completing the single-player objectives. The cooperative campaign's mission progression continued forward after the completion of each mission, regardless of which team won.
There was also the 'anarchy' mode, which was basically Shattered Steel's term for deathmatch. Anarchy could be played in both FFA and team-based modes. Anarchy mode also supported bots for offline play and filling in player slots.
Patch 1.14 was effectively the expansion for Shattered Steel. Alongside this patch, Bioware released a mission editor and two additional campaigns for the game. These additional campaigns could only be accessed through the game's multiplayer menu and selecting the cooperative option. The campaigns were labeled worlds 5 and 6 in the cooperative's world select option.
Just like the cooperative options for the single player campaign, both campaigns could be played competitively as well. World 5 ran with this option extensively, as it is a purely competitive campaign that takes place before the events of Shattered Steel's single player campaign.
World 6 is an actual stand-alone cooperative campaign, seemingly picking up where the original campaign ended.