I was having a discussion with a friend about what a RPG 'really' is, what defines it from any other genre. Most, if not all, computer games are role-assuming games, and story-driven to some extent. So what tips the scale between a RPG and, say, an action game?

I reasoned that it was the focus of the gameplay which decided a genre, for example a shooter is a game with emphasis on shooting, and thus a RPG had a focus on role-playing or story.

My friend argued that it was the 'systems' which defined the game genre. He seemed to think the basis of them was to do with skills based, for RPGs, and the amount of story was irrelevant.