For those of you who have never played a metal gear game, A metal Gear is a Bipedial tank capable of launching a nuclear missile form any terrain. The project was started by the Russians durring the cold war to get an edge on the americans ICBMs. There are many varriations of the Metal gears these are the best of the best right here.
Metal Gear TX-55

This baby right here was the first ever American made metal gear. It was slow and clumbsy but it was a hand full when only armed with a rocket launcher and several Grenades.
Metal Gear D

This was possibly the easiest Metal Gear I ever took down. Its basically the Metal Gear TX-55 with a added rocket launcher.
Metal Gear REX

The Greatest Metal Gear yet. Armed with a rail gun it was nearly impossible to beat this thing. The missile guidence system? Amazing that thing was locked onto me before I could move. It was trully a work of art. whee
Metal Gear Ray

The Metal Gear Ray was trully a work of art as well. It was capable of inflitrating an enemy base and blasting them to bits. The only flaw was they were built for speed, Thus their legs were light and hallow. If you could hit them in the leg with a rocket they would pretty much be out of luck.
Shagohod

I'm not really sure if this counts as a Metal Gear but the design is at the core of every metal gear. It was slow and clumbsy but considering it was built in the 1960s it was way ahead of its time.