Before the advent of Metal Gear, all action/adventures were quite straightforward: Go Forth, and Let The Trigger Twitching Commence.

And then Metal Gear came. You're still trying to pull the same stunt? You're dead, pal, you're dead.

Metal Gear Solid's subtitle summarises best what the series is all about: "Tactical Espionage Action". The hero of the games, Solid Snake, is a surprisingly realistic action hero: If he takes couple of bullets, he won't be breathing any longer. And his enemies are (more or less) equally mortal - except that they're there in numbers. Alert.

Snake needs to use the trigger, yes, but violence is never the big factor in MG series. The games are actually about sneaking. Snake is a covert operative, not an one-man army. The trick is to stay hidden and kill noiselessly. Thus, the games are extremely tactical. Use eyes, make decision, and run in the shadows.

"Big Boss here. Your mission is to infiltrate! Be careful not to let enemy detect you."

- Big Boss,
Metal Gear (Engrish NES version)

And what's "Metal Gear", then? It's a new generation super weapon. Think of a 'Mech with a nuclear weapon as its heaviest armament. Snake's mission is to destroy it (at least in MG and PS/GB versions of MGS.