Mech Commander Gold includes the original Mech Commander along with the new campaign Desperate Measures and several improvements, including completely new terrain, new mechs, and multiple difficulty settings. It also includes an editor to design your own missions.
Mech Commander itself is an isometric real-time strategy game with the persistence of the Mechwarrior role-playing. As you lead your lance through missions, their skills would grow, you'll salvage/capture more mechs, more weapons, and so on and so forth.
Originally, Desperate Measures was going to be released as a separate expansion pack. However, retailers by then want "gold" packages, so MicroProse made MechCommander: Gold. However, they didn't have time to update all the printed documentation. All of the printed manuals, reference cards, etc. refer to Deseparate Measures, and a separate sheet tells the players to "substitute MechCommander Gold for all references to MechCommander: Desperate Measures".