MGS, not only gave new life to the series...it actually granted Solid Snake Immortality! "There can be only one!!" hehe
This was one of two games that created the stealth genre on PSX. I can never remember of this came out first or if it was Tenchu, but it doesn't matter. Either way a genra was created that has spread throughout the gaming industry like wildfire. Only Max Payne's "bullet time" has been ripped off more....(yes i'm talking to you sam fisher).
Anyhoo, not counting the excellent stealth engine, the story happens to be a masterpiece as well. It fast became the bedrock for the four subsequent sequels plotlines.
The gameplay is tight, the graphics were exceptional for the time, the bosses were were innovative, and you cared about what was going on.
Bottom line, if you haven't played this game, I question your validity as a gamer.