All of Vallejo's paints are derived from the same basic formula in that their special solvent-less thinner and other auxiliaries are compatible across the board.

The GameColor is said to have a slightly "tougher" finish in terms of holding up to a lot of handling and knocking around.  IMO I think they are essentially the same as ModelColor, except the colors, or rather the names of the colors, cater to the table top gaming crowd.

ModelAir of course is quite different in that it is much thinner that the others, and no colors in that line contain hazardous pigments (there are a limited number of ModelColor colors which contain cadmium).