F.E.A.R.? Doom 3? Those games are for kids, or at least when you compare them to System Shock 2.
It's simply the most intense game I've ever played. Interestingly, the little tricks that make System Shock 2 as good as it is are gameplay mechanics often criticized in other titles. We'll get to that later.
System Shock 2 begins 67 trillion miles from Earth, where starships Von Braun (the first faster-than-light ship ever) and Rickenbacker (Von Braun's escort) are overtaken by an unknown force which turns most of its crews into mindless humanoid monsters filled with alien tissue and robotic enhancements. You start off some time after the incident, waking up from a post-operative cryogenic sleep. Rather conveniently, your memory restoration process fails. Your only contact, Dr. Janice Polito, tells you via voice mails that you volunteered to get cybernetic stuff buried in your head.
And thus begins your journey into the bloody corridors of the Von Braun and the Rickenbacker. The game plays as an FPS/RPG crossover with heavy emphasis placed on atmosphere and survival as an objective. You won't find yourself gunning down hundreds of aliens here. Rather, you will find yourself running away from the next wave enemies as you accidentally trigger a security alert while your gun is on the verge of jamming and you have less than 10 rounds left.
Yes, that last sentence almost sums up the most important gameplay mechanics which makes System Shock 2 stand out. First, you have very little ammo. While you can purchase ammunition, it is quite costly, especially when Nanites (the game's currency) are also used for other purposes, such as hacking security computers, healing yourself with surgical units, or even resurrection through quantum regeneration.
Second, your weapons break down over time. While many players have criticized the speed at which weapons deteriorate, I find it very suitable to the mood of the game. This feature forces you to invest some points in the maintenance skill and makes inventory management critical to your success. Moreover, it combines nicely with the lack of ammunition and sends a message to players: make every shot count!
Finally, your enemies respawn after some time. A trip through an area you cleared out 30 minutes ago may prove deadly as those enemies have come back, and sometimes with better weapons. Security alarms will trigger a period in which enemies continuously spawn from each spawn point, forcing you to adopt more defensive (or even evasive) strategies until the alarm period is over.
The rest of the game's features have become rather commonplace today. Doom 3's audio logs-based "they-were-here" storytelling technique is here in full force, and arguably remains the best example of such technique. Scripted sequences (ghosts!) are scattered here and there, used to augment the creepy atmosphere and, in some cases, provide hints. You can even find minigames to play on your Multi-Function Display interface, much like the way you play arcade mini-games in Grand Theft Auto: San Andreas.
Overall, the game has impressive production values. The stunning sound design, which places much greater emphasis on effects and voice acting than music, is scarily effective. From the call of the midwives to the screech of the psychic monkeys, System Shock 2 sounds absolutely perfect. The visuals are good enough to evoke a creepy atmosphere, although the character models are rather on the low-poly side.
As System Shock 2 has heavy RPG elements and gameplay mechanics which encourage an emergent style of play, it's far more replayable than most single-player shooters. You can choose from three distinctly different classes and upgrade your abilities as you progress through the game. Most situations can be solved by more than one way, and the constantly respawning enemies keep you on the edge of your seat all the time. And there's even a co-op mode where you can play through the single-player campaign on Hard difficulty with up to three of your friends. Pretty impressive for an old title, I think.
Playing System Shock 2 now makes me feel rather nostalgic. Innovation is something seriously lacking in the gaming industry today, and the notion that a 6-year-old title has more innovation packed into it than a dozen recent titles combined seem absurd. Despite a heavy defeat in technical aspects, System Shock 2 remains today the best first-person perspective game of any kind ever made. And definitely the most scary one.
Now try to find a copy of the game and buy a lot of underwear. Just in case you soil your pants. I know I almost did.