The first generation of pokemon was hugely popular that kicked things off.
They were conservative and designed gold and silver so it would be just like red and blue (can't blame them)
Then the pokemon company was established and they knew that they couldn't keep releasing the same game over and over again so they went to the drawing board. They went liberal with ruby and sapphire and made some big changes. They added running, good color, better sound etc. they also added the most pokemon in this generation than any other to make it fresh. hey added harder puzzles and stuff because their fanbase was getting older. Better music etc. oh and they added double battles
4th generation they were trying to get back to second generation days and it worked. They have a lot of evolutions for 2nd ge pokemn and the game itself wasnt a hugechange from ruby and sapphire other than better graphics.
5th generation is going liberal again. the battle system has got a lot more complex. they added triple battles and random wifi battles. they recently said that there will be no od pokemon until youbeat the gam to keep things fresh...similar to ruby and sapphire. the characters in black and white are older and is an overall more mature game like ruby and sapphire. plus they are similar because both games have a dessert :D discuss