Metal Gear Solid (Playstation, 1998)

When I was in middle and high school, M (for Mature, 17 or older) rated video games were the coolest games.  I had friends who fawned over Halo and Grand Theft Auto and laughed at me when I talked about playing Mario.  E (for Everyone) and T (for Teen) rated games were for babies, and M rated games were what the cool kids played.  Games filled with gore, cursing, and sex.  What I realized years later was that many of these "cool" M games were not, well, very good.  The developers probably filled them with all that stuff so that adolescent boys would buy them.
Hideo Kojima's Metal Gear Solid (1998) is not one of those games.  There are no flashy lights or distractions here, just substance.  It broke new ground in terms of gameplay, graphics, and storytelling.  You took control of the genetically enhanced super soldier, Solid Snake, and your mission was to infiltrate the nuclear weapons facility run by the terrorist group FOXHOUND, rescue two hostages, and stop the missile launch.  Snake is equipped for the job with a handgun, codac (a tiny radio planted on his eardrum that only he can hear), and... cigarettes? "I hid them in my stomach," Snake tells his superior officers when they learn that he smuggled them past their screening.
This was the most cinematic game for the time when it came out.  The game plays and feels like a great spy movie.  Each character is fleshed out and is given superb dialogue and personality.  Snake is easily the best among the cast.  He is incredibly smart, fast, and ruthless, but can also be sympathetic and kind of a wise-ass.  The more you learn about each character and FOXHOUND, the more you come to realize that there is something far more sinister happening than anyone could have expected.
One of the hostages is the DARPA chief, and in a cinematic conversation between him and Snake, he reveals that the terrorists are secretly building Metal Gear, a walking tank that can fire nukes from anywhere. After Snake gains this information, the DARPA chief mysteriously convulses and dies.  The same thing happens when Snake rescues the ArmsTech president, who tells Snake about one of the FOXHOUND leaders, Psycho Mantis, a master of psychokenesis.  Metal Gear Solid has a deep and complicated story that is constantly engaging and suspenseful.
Snake must navigate the facility while avoiding detection by the many genome soldiers.  This is the main mechanic of gameplay.  While brute force is possible, stealth is by and far the preferred route.  Ammunition and health rejuvenating rations are limited, and soldiers will call in overwhelming reinforcements, so it is best to avoid confrontation.  Enemy soldiers are not easy to elude, though.  Snake may leave footprints in the snow that a soldier will follow.  Stepping loudly on metal will give away your position.  Surveillance cameras are posted in many rooms.  Sometimes you have to be more clever than the soldiers.  You can tap on a wall and run someplace else to throw them off.  You may hide in a cardboard box where appropriate.  Hiding under equipment and in shadows is effective.  When Snake is spotted, you must escape from sight and find a place to hide until the enemy lowers the warning level.
When Snake is forced to fight with FOXHOUND's special forces, every confrontation is memorable.  There is the sniper fight with Sniper Wolf during a blizzard, the handgun fight with Revolver Ocelot in a room that is armed to detonate, and a battle with Vulcan Raven, who is riding in a tank.  The most memorable of all is the battle with Psycho Mantis, who reads your mind and preempts your every move.  The secret is to plug your controller into the second port.  In every way, this game invented, improved, and set the bar higher for video gaming.