The Metal Gear Solid series is my favorite series ever. The director of the series Hideo Kojima sort of molded the main character Solid Snake after Kurt Russell's character from the movie Escape from New York, Snake Plissken.
The gameplay is supposed to be about sneaking and stealth, but you can play guns blazing if you want. The story is the #1 selling point in the series though. They're all about some organization gaining control of a walking tank called Metal Gear that has the ability to fire nukes from its rail gun. Your job in all the games is to stop said terrorists. It's very sciencey though, with a lot of the plot based around cloning, nanomachines to control soldiers emotions and health, weapons of mass destruction. And it's also very political, with a lot focusing on war and what the world is actually controlled by.
The story is very deep and the cutscenes are really long. Start with Metal Gear Solid on the PS1, which you can download from the Playstation Store for like $10. Then pick up the Metal Gear Solid Collection on either 360 or PS3 and play Metal Gear Solid 2, Metal Gear Solid 3 and if you want, Metal Gear Solid Peace Walker (but that one isn't that essential, and the gameplay isn't anything like the other games). Then pick up Metal Gear Solid 4 and behold one of the most amazing looking games on the system. If I remember right, it has about 8 hours or so of cutscenes. Throw in gameplay and it'll take you about 20 hours or so to finish, that's how long my very first playthrough was.
None of the games have online play though (except Peace Walker, but it's co-op). MGS3 and MGS4 used to have Metal Gear Online, but those didn't last very long.
