The Metal Gear series may not be quite as iconic as something like Mario or Pokemon, but titles like this show that it has every right to be and then some. MGS3, quite simply, is everything a video game should be and has nothing that a video game should not have.
It draws you in immediately. Fans and newcomers alike can connect to the story with no prior knowledge of the series because it uses a famous historical conflict as the backdrop. Though the cutscenes in the beginning are a little long, they manage to set up a complex plot without using any of the jargon or pseudoscience of the later games. The tutorial part of the game does a fine job in setting up the plot in an exciting and cinematic fashion and getting the player used to the controls in a somewhat more controlled environment while at the same time being completely unintrusive to series veterans.
Its gameplay is sublime. You have an absurd amount of options to approaching almost any given situation, more than almost any game I've ever seen, and all of them work beautifully. Do you want to simply sneak past the guards? No? How about throwing an empty magazine to upset their patrols, taking one hostage to make sure his friends don't shoot you? Does that not suit you? Then how about throwing live snakes at them or blowing up their food supplies and giving them poison mushrooms? Still no? Then why don't you send some fucking bees after them or scare them off by wearing a crocodile head-shaped hat and peeking around a corner, making them think you're a crocodile-man? Boss fights have fewer options (though still quite a number for some), but make up for it in spectacle.
Its atmosphere has to be experienced to be believed. The game has all the charm of the spy films it emulates, but keeps its central characters human enough to make all the tension the story builds work. Every part of the soundtrack has its place, whether it be low key jungle noises for sneaking or sweeping orchestral themes for climactic battles.
While I'm almost certainly overselling it here, I don't believe I am by that much. I do see flaws within MGS3, but they are so miniscule compared to what it does right that the game might as well be perfect. No game I've played has ever done so well in every single regard, and I doubt I'll ever play another game that comes as close to perfection again.