You unlock Stealth Camouflage (i.e. Invisibility Cloak, Predator Camo, etc.)
The FROGS in the game Metal Gear Solid 4 are not robots but humans.
The FROGS on the game Metal Gear Solid 4 are female soldiers not male soldiers.
Eat them for Stamina.
power ups or target practice
If you mean story wise then I believe it goes: Metal Gear Solid 3: Snake Eater Metal Gear Metal Gear 2: Solid Snake Metal Gear Solid Metal Gear Solid 2 Metal Gear Solid 4 But I may be wrong, and that isn't counting either of the Portable Ops games.
nothing
metal gear solid1, metal gear solid 2 sons of liberty, metal gear solid 3 snake eater, and metal gear solid 4 guns of the patriots.
Metal Gear Solid, Metal Gear Solid 2: Sons of Liberty and Metal Gear Solid 3: Snake Eater
he survives
Metal Gear Solid happened in 1998.
Metal Gear Solid 4: Guns of the Patriots
The best Metal Gear Solid game is what you define as 'best'. Personally, I think Metal Gear Solid 4: Guns of the Patriots is the best Metal Gear Solid game, it is also the highest rated Metal Gear Solid game ever to be developed and published.