I love RPG's because of the sense of progress you get; you overcome certain challenges, and the numbers get bigger, or you get more skills or whatever. So if an action game has some light RPG elements, I'm more likely to give it a try.
They're in general also heavier on the story aspect than most other genres (apart from adventure games, and some other notable exceptions), and I play games mainly the same way I read a book or watch a film, to see what happens next, and to know how it all ends.
I prefer WRPG's, because the grind is often less boring, but I've played some damn good JRPG's too.
My favourites are the old top down Infinity Engine games: The Baldur's Gate series, The Icewind Dale series, and Planescape: Torment. No other games come even close.