Experience points or something analogue, and being turn-based or semi-turn-based. A degree of customization is important too but not to the point of defining the genre.
That's for me at least. So I don't consider Zelda, Monster Hunter, Mass Effect, Elder Scrolls etc. to be RPGs. Dragon Age and FFXII would make it though, since that's what I'd consider to be semi-turn-based.







