As in its predecessor, System Shock, gameplay in System Shock 2 is an amalgamation of the action role-playing game and survival horror genres. The developers achieved this gameplay design by rendering the experience as a standard first-person shooter and adding a character customization and development system, which are considered as signature role-play elements. The player uses melee and projectile weapons to defeat enemies, while a role-playing system allows the development of useful abilities. Navigation is presented from a first-person view and complemented with a heads-up display that shows character and weapon information, a map, and a drag and drop inventory.
The backstory is explained progressively through the player's acquisition of audio logs and encounters with ghostly apparitions. At the beginning of the game, the player chooses a career in a branch of the Unified National Nominate, a fictional military organization. Each branch of service gives the player a set of starting bonuses composed of certain skills, though may thereafter freely develop as the player chooses. The Marine begins with bonuses to weaponry, the Navy officer is skilled in repairing and hacking, and the OSA agent gets a starting set of psionic powers.
The player can upgrade their skills by using "cyber-modules" given as rewards for completing objectives such as searching the ship and then spend them at devices called "cyber-upgrade units" to obtain enhanced skills. Operating system (O/S) units allow one-time character upgrades to be made (e.g. permanent health enhancement). An in-game currency called "nanites" may be spent on items at vending machines, including ammunition supplies and health packs. "Quantum Bio-Reconstruction Machines" can be activated and reconstitute the player for 10 nanites if they die inside the area in which the machine resides. Otherwise, the game ends and progress must be resumed from a save point. The player can hack devices, such as keypads to open alternate areas and vending machines to reduce prices. When a hack is attempted, a minigame begins that features a grid of green nodes; the player must connect three in a straight row to succeed. Optionally, electronic lock picks, called "ICE-picks", can be found that will automatically hack a machine, regardless of its difficulty.
Throughout the game, the player can procure various weapons, including melee weapons, pistols, shotguns, and alien weapons. Non-melee weapons degrade with use and will break if they are not regularly repaired with maintenance tools. There are a variety of ammunition types, each of which is most damaging to a specific enemy. For example, organic enemies are vulnerable to anti-personnel rounds, while mechanical foes are weak against armor-piercing rounds. Similarly, energy weapons cause the most damage against robots and cyborgs, and the annelid-made exotic weaponry is particularly harmful to organic targets. Because ammunition is scarce, to be effective the player must use it sparingly and carefully search rooms for supplies.
The game includes a research function. When new objects are encountered in the game, especially enemies, their organs can be collected and, when combined with chemicals found in storage rooms, the player can research the enemies and thus improve their damage against them. Similarly, some exotic weapons and items can only be used after being researched. OSA agents effectively have a separate weapons tree available to them. Psionic powers can be learned, such as invisibility, fireballs, and teleportation.
Plot
Backstory
In 2072, after the Citadel Station's demise, TriOptimum's attempts to cover up the incident were exposed to the media and the corporation was brought up on charges from multiple individuals and companies for the ensuing scandal. The virus developed there killed the station's population; the ruthless malevolent A.I supercomputer named SHODAN controlled, and eventually destroyed the Citadel Station in hopes of enslaving and destroying humanity. After a massive number of trials, the company went bankrupt and their operations were shut down. The United Nations Nominate (UNN), a UN successor, was established to combat the malevolence and corruption of power-hungry corporations, including TriOptimum. Artificial intelligence was reduced to most rudimentary tasks in order to prevent the creation of another SHODAN-like malevolent AI, and development of new technologies was halted. Meanwhile, the hacker (the original game's main protagonist), who became the most famous person in the world, vanished from public eye.
In 2100, 28 years later, the company's failed stocks and assets were bought by a Russian oligarch named Anatoly Korenchkin, a former black market operator who sought to make money in legitimate ways. He re-licensed and restored the company to its former status in the following decade. Along with producing healthcare and consumer products, Korenchkin signed weapons contracts with various military organizations, private and political-owned. The new UNN was almost virtually powerless with Korenchkin exercising control over them.
In January 2114, 42 years after the Citadel events and 14 years into rebuilding TriOptimum, the company created an experimental FTL starship, the Von Braun, which is now on its maiden voyage. The ship is also followed by a UNN space vessel, the Rickenbacker, which is controlled by Captain William Bedford Diego, son of Edward Diego, the Citadel Station's infamous commander and public hero of the Battle of the Boston Harbor during the Eastern States Police Action. Because the Rickenbacker does not have an FTL system of its own, the two ships are attached for the trip. However, Korenchkin was egotistical enough to make himself the captain of the Von Braun despite being inexperienced.
In July 2114, 5 months into the journey, the ships respond to a distress signal from the planet Tau Ceti V, outside the Solar System. A rescue team is sent to the planet's surface where they discover strange eggs; these eggs, found in an old ejection pod, infect the rescue team and integrate them into an alien communion known as "the Many" - a psychic hive mind generated by parasitic worms which can infect and mutate a human host. The parasites eventually spread to both ships and take over or kill most of their crews.
