If I bought say, a Mametchi Tama-Go... then the seperate Mametchi toy, would I get the same game and the only difference be the figure and the face cover?
You would not get the same game. The figurines that come with their respective Tama-Gos, called "lite" figurines, only contain one game, Cradles. If you were to buy the separate "full" figurines, those each come with two completely different games, a shop with different items, and other exclusives. Check out this helpful LIST of information regarding the figurines!