The most hardcore MGS4 players are going to go for the Big Boss
achievement trophy emblem, which requires masterful play with no deaths, no alerts, no kills, no recovery items, no stealth suit and no special items. To get the emblem, the entire game must be completed in 5 hours, but Tyndis from YouTube has managed to do it in less than three hours.
Obviously, because the entire game can be seen in these videos, it should be obviously that this is one giant spoiler. If you haven't beaten the game yet, come back to watch it later. But for those that want to see Metal Gear greatness, enjoy.