Pokemon Gold/Silver games are continued from the Green, Yellow, Red and Blue versions. In these two versions there wil be new cities and over 100 new Pokemon. The newer Pokemon will have better moves and abilitys so you won't get bored of using the same moves from every other game. Also you will have a scateboard to go along with your bike and there may be other new forms of transport as well. There's gonna be different seces of Pokemon as well like Nidoran male/female except this time you will be able to breed and produce new kinds of Pokemon! There will be night and day as well so that mean Pokemon you can only catch at night and day.
You will still be able to swap Pokemon but if you transfer a new type to the Red or Blue catridge it will go down an evolution. Eg A Pikablu traded to Red or Blue would probably go back to a Richu/Pikachu get it? The game will also be Color Gameboy compatible so you can see all your favorite Pokemon in color! These games should come out in America about April or May '99.