You know, there was a time when all this genre-labeling was a lot easier.
Even if the terminology has changed, and even though we have far more diversity than at any other time in the industry's history (let's not forget the dawn of gaming), everything is starting to blend together. I always used to look at a shelf and go, "That's an RPG and that isn't." It was just so obvious.
I mean, action games didn't have levels or experience. You could rarely equip things besides some weapons you might pick up. There was no big ol' world to explore. Now you look at something like Assassin's Creed and the role-playing elements are everywhere. Just about the only thing missing is an experience/level-up system; include that, and how is it not an RPG? But it's not even that easy; there are levels in all sorts of games now, including shooters. Furthermore, with the death of "old-fashioned" mechanics unique to RPGs (like original turn-based systems such as The Judgment Ring in Shadow Hearts or the Arts in Legaia ), just about everything is in real-time.
So you get something like the upcoming Bioshock Infinite , which is definitely a blend of role-playing and FPS, as was last year's Deus Ex: Human Revolution . But even games that have no business being even close to the RPG genre, such as something like The Last Of Us , does have role-playing aspects we thought we'd never see in action-oriented adventures. The bottom line is that with all this blending and mixing, the lines are blurred and precisely labeling any given game is getting tougher and tougher. So many are simply trying to do living, breathing worlds better than the next, so elements from all genres are often easily found.
Maybe the last easy-to-label genres are the Fighting and Sports/Racing categories. But after that…things get awfully muddy.