System Shock is often credited as an FPS pioneer, which makes sense because it takes place from a first-person perspective and there is indeed shooting in it, but what it really is is, being a sci-fi successor to the Ultima Underworld games, is a real-time dungeon crawler. You wake up on a space station orbiting Saturn and have explore the environment, battling hostile monsters while SHODAN, the evil AI controlling the station, throws challenges at you like an unsympathetic DM. A major change from the Underworld games was to get rid of NPCs to talk to because the designers felt it broke immersion, so to impart the story to the player they came up with the concept of audio logs left by departed crewmembers. Audio logs have been used so often since Bioshock was a hit that they've become a creaky cliche, but they were very interesting in System Shock because they gave the player the sense of piecing things together like a puzzle and a sense of how to crack Citadel Station's mysteries.
System Shock's actual story is a bit like a cyberpunk take on Die Hard. You're one guy up against a master villain and her minions in an enclosed space, having to scrounge for weapons and resources to foil her schemes while some desperate people on Earth occasionally beam messages to you. A couple of unusual wrinkles are that the hacker you control is amoral and basically caused the whole mess in the first place by scrambling SHODAN's programming, causing her to become self-aware and develop a god complex, and SHODAN herself is a memorable antagonist. Most of the voice acting in the game is amateurish, being handled by non-actors who just worked at Looking Glass, but somehow Terri Brosius, another non-actor (albeit a professional musician) aided by a lot of Max Headroom-like audio mixing, hit on a perfect mix of sultry menace and batshit insanity.
System Shock's controls and user interface are notoriously complex. Again, the game wasn't meant to be an action game, it was a dungeon crawler, so the designers weren't thinking in terms of a smooth, fast, high-octane thrillride like Wolfenstein 3D. They were thinking in terms of player immersion, so they tried to give players as much control over the hero as possible, which meant stuff like allowing you to stand upright, crouch, or lie prone while doing all those things while also leaning left or right while also allowing you to manipulate stuff in the environment or your inventory like you do in RPGs or adventure games while also running, jumping, or climbing all over accessible surfaces. There are positives and negatives to it. The degree to which they succeeded is remarkable for the time and at its best the game is indeed very immersive, but until you fully master the system it does come across as overly fiddly and overwhelming, and even when you do master it the game still makes you feel like you're piloting a human-sized mech rather than a person who simply does what you want. Then there's the cyberspace aspect of the game, which was based on Looking Glass's engine for the Flight Unlimited flight simulator and introduces control challenges of its own. All in all, though, it's a first-rank, highly replayable classic.
