There are now 17 Metal Gear Solid games. (Correct at time of writing)

MGS2 - sold over 7 million copies world wide. Average rating - 96%

MGS1 - sold over 6 million copies ww. Average rating - 94

MGS3 - sold over 3.6 million copies ww. Average rating - 91%

Metal Gear/MSX

Metal Gear 2: solid snake/MSX

Metal Gear Solid/PS1/PC

Metal Gear Solid: Integral PS1/PC Also known as Metal Gear Solid Special Missions

Metal Gear Solid: The Twin Snakes/GameCube

Metal Gear Solid 2: Sons of Liberty/PS2

Metal Gear Solid 2: Substance/PS2/Xbox

Metal Gear Solid 3: Snake Eater/PS2

Metal Gear Solid 3: Subsistance/PS2

Metal Gear Solid 4: Guns of the Patriots/PS3

Metal Gear Solid:Ghost babe/GameBoy Colour

Metal Gear Acid/PSP

Metal Gear Acid 2/PSP

Metal Gear Solid: Digital Graphic Novel/PSP

Metal Gear Solid: Digital Graphic Novel 2/PSP

Metal Gear Solid: Portable Ops/PSP

Metal Gear Solid: Portable Ops Plus/PSP

Metal Gear Solid: PeaceWalker/PSP

Metal Gear Rising: Xbox360/PS3

That's a lot of Metal Gear....