Good post on What Games Are about the derivative nature of games and their detractors:
It’s hard not to notice that some games have roots in other games and that genres tend to group around certain rules. In some cases these rules even become a template and lead developers to copy each others’ work wholesale. Cloned games are the mark of either student or lazy developers, however sometimes a game comes along which takes its start from another game type but runs with it and becomes something original. The negative backlash then says ‘Oh that game is just a copy of X’. Like a bunch of haughtier-than-thou music fans striving to be more underground than one another, this kind of one-upmanship is just jealousy talking.