Ah my area of expertise, the plot of all the Metal Gear games
But yeah I have MGS on GBC, it's a good game I think, follows the MGS style well.
Released in 2000 for the Gameboy Color, and originally named Metal Gear: Ghost Babel (name of the Japanese release), the name was changed for European and American releases for marketing purposes and the recognition the name had gotten due to the Playstation version.
The story is set seven years after Outer Heaven in 2002, and Snake is brought in after a US Army cargo plane carrying nuclear weapons and a new Metal Gear is hijacked and held by terrorists in the Central African nation of Gindra, led by the GLF, the Gindran Liberation Front. They and their leader, General Augustine Eguabon (the developers really do have fun making up these names....) demand independence for Gindra and withdrawal of United Nations peacekeepers or they will use Metal Gear (which was developed by the US government after the retrieval of plans from Outer Heaven) to fire a nuclear weapon. A Delta Force team is set in and wiped out, prompting Snake to be asked in after Campbell reveals that the land the Gindra fortress, Galuade, is on is the same place as where Outer Heaven was situated seven years before, leaving Snake to head to Outer Heaven again to stop Metal Gear. Here, he works with Sergenant Chris Jenner, the only survivor from the Delta Force squad sent in and James Harks, the young designer of the Metal Gear housed in Gindra to take on the terrorist group Black Chamber who were working with the GLF and eventually head down to the 100th basement floor again to face Metal Gear, Black Arts Viper (the leader of Black Chamber) and the General.
The story has large similarities with the Playstation version as well as Metal Gear, but is also a very good standalone story, despite not being part of the official Metal Gear history (although not so apart from it as Snake's Revenge is). The graphical limitations of the Gameboy Color let the game go back to it's MSX and NES roots of graphic style, but still manage to work well, still keeping certain elements of the Playstation version, such as being able to back against a wall and the same basic weapons as well just with different names (SOCOM = 5-7, FAMAS = R5). It evens includes a VR Training section that is much the same as the one on the Playstation in content, as well as a 2 player feature using the link cable. No other Metal Gear games have a multiplayer feature.