I remember discussion with a friend, ages ago on about music and genres.
We started counting sub-genres for so called "electronic music" and then for broadly accepted bag for anything that's Rock.
Then quickly we realized that this discussion has no sense and we finished it with a joke "so.. if a music genre has more subgenres then it's richer in listening experience, right?"

Same silly discussion started with couple of my fellows, but on game genres. It started with rambling like "sniff, sniff, point&click adventure games are long dead". That's not true, however discussion went further to: "that's adventure; no.. that's rpg; no that is.." whatever it's, it doesn't make sense to split it to whaveter names we would like to pick up for a definition.

I strongly believe that sticking to hardcore definition of a particular atomic genre is pointless.
Nevertheless,analysing where particular features typical to a that atomic genre mix with another is valuable. That's really good lesson to learn how in a evolutionary way new cool games and "genres" are defined. I believe that genre naming should be left to the press. They like to name a mish-mash whatever they think it is. Take rts-rpg or other combo-styled genres as an example.

From game-designer perspective core thinking should go around features, combining them, testing playability and then, heck, let's call it a new genre if neccessary.

If we go around rpg-adventure combination as one example of natural end-product assembled from prime-elements, what we see?

RPG side has been well defined recently on Gamasutra as a game on leveling, dungeon/fantasy world crawling, combat&magic system put into nice gameplay and sometimes having deeper story. Story from otherside is in common with adventure game where all is about storytelling and puzzles.

If to this combination I add some real-time action, I dare to say that GTA IV is a gangster story themed RPG game but with very weak character stats development.

I have there totally no visible option to grow my dexterity, strength and other attributes.
I have limited access to cool items beside one particular type - a ride. Here I have pleanty options to hijack something (so my Class is Rogue then).

As for a ride, I don't have quasi-medieval world typical horses like in Oblivion.
I have cars, of course I have, as it's gangsta game for fireball's sake.
I have more options for taking that ride than a single horse in fantasy scheme, yet I don't have (again) much options to pimp it up. 

Maybe that's good design choice anyway, I'd be really worried, if Rockstar made a magic armor as a paid DLC for my fast muscle car I drived on Liberty City streets..

Still an RPG.. or better.. who cares about genres, I more likely recommend picking up all what's best from all of atomic genres, then mixing them feature by feature if that makes sense.