10. Stealth Camo - Metal Gear Solid
Hideo Kojima's Metal Gear Solid is unquestionably one of the greatest games of all time, yet as stunning as that initial play-through absolutely is, things get even better once you've beaten the game and unlocked an extra goodie or two.
What players receive upon completion is dependent on whether or not they successfully resisted Revolver Ocelot's torture mid-way through the game.
Button-bash your way to success and you'll receive a bandana for your second play-through, giving you infinite ammo. If you submit, however, you get something much cooler.
"Failing" the torture sequence results in Otacon giving Snake stealth camouflage at the end of the game, which can be used at will during your next play-through, aside from in boss fights and scripted sequences requiring an alert state.
Needless to say, stealth camo allows players to freely explore the game's iconic environments (mostly) free of disruption, and makes an already ludicrously entertaining game even more fun.
Though completing Metal Gear Solid a second time on the same save file will unlock a tuxedo for Snake, the camo's literally game-changing properties can't be beaten, as it basically reinvents the entire experience.