Let's exclude all turnbased and linear role playing Action role playing games for now. They share more in common with Strategy and Action games than Action-Adventures.

Now at the base of it, what differentiates an Action-Adventure, from an Action Role Playing game with just as or more exploration. I want to talk strictly gameplay, and don't want anything to do with Story or any other non gameplay aspects. From the looks of it. Role Playing Games seem to have more customization aspects, but you see that in Action-Adventures as well. Also, these customization aspects do not define "Role Playing". Also at what point would you say that this game doesn't have enough customization to be a Role Playing Game? I find this way of going about things very relative.  Is it leveling? That makes very little sense to go about things, because in Action-Adventures you level as well. Maybe not in the same stat based system, but you do level. Is it the puzzle aspects of Action-Adventures? This also makes very little sense. Not only is there Action-Adventures without puzzles, but there are games from every genre with them. Definately not a distinguishing characteristic. Is it combat? If so, what area of combat? I don't think this could be it either. Early Action-Adventures shared pretty much the same combat as Action- Role Playing games of the time.

So what is it that distinguishes the two?

I think the only valid answer to this questions is how you upgrade your equipment and abilities. In Role Playing games as well as other genres, you find new equipment and change it at any time. In Action-Adventures you upgrade your equipment. In Metroid you upgrade your Suit, Visors, etc. In Zelda you upgrade your sword, clothing, etc.

Having said this, I still don't think it is enough to distinguish Role Playing games as their own Genre. It seems to me that the similarities between Exploration Role Playing games like Oblivion, Fallout and Action Adventures like Zelda, Metroid are far to similar than different.

Now let's move on....

What makes a Turn Based Role Playing Game different from a Strategy game from a gameplay aspect. Remember this: Strategy games do NOT have to be part of the RTS, TBS, or SRPG genres. They also don't have to be mission based. They do not have to be linear either. What makes a Strategy game imo, is the Combat more specifically the Micromanagement.  Both of these features are present in Turn Based Role Playing games. To prove my point even further that Strategy games don't need to be mission based or linear, I will note two very famous, recent innovations in the RTS sub-genre. These two games are Pikmin and Little King Story. There is a lot of debate which genre these games would fit into, but from a taxonomical point of view, it would seem that they would fit into the strategy genre. They might even be different enough to creat a sub genre. Little King Story and Pikmin are both Quest and Exploration based rather than Mission based, and they have both aspects that I mentioned. So I think it is safe to say that Turn Based Role Playing games should fit into the strategy macrogenre, as a sub-genre. 

Finally, I will mention linear Action Role Playing games. These are the games without an overworld, and do not have much exploration. Examples of these are Final Fantasy Crystal Chronicles up until Crystal Bearers, Kingdom Hearts, and Crisis Core Final Fantasy VII. For these games, I don't see much of a difference from Pure Action games, and most notably the Hack N Slash genre. The basic gameplay is pure combat in this example. You mostly kill enemies, and progress in a linear fashion. Sometimes there is a simple puzzle or two, but you just keep going most of the time until you reach the ending. I can't note any differences other than the extra customization that you find in a ARPG. Other than that, to me they seem the same.

So to conclude, I find the Role-Playing Genre more of a collaboration of Genres held together by an extra level of customization, as well as the ideal of a large focus in the Story. Otherwise, from the gameplay point of view, it isn't a single genre, nor are the games excempt from the real genres they fit into. Anybody want to argue my points? Agree? Agree with some things, while disagreeing with others? Anything else you want to sum up that is relevant to the topic at hand?

Seems like your problem is with "new age" rpgs, not real rpgs. Look at real rpgs from the nes/snes/ps1 era, those were original rpgs and are their own genre. New action adventure rpgs like oblivion, are exactly that, a mix of several genres.

Well the Action-Adventure genre rooted from these RPGs. Zelda isn't much different from say Ultima, Wizardry, Secret of Mana, or tons of others from the Pre-NES, Nes, Snes, and PS eras.

Guess it's opinion then, I think Zelda is wayyyyy different from games like Secret of Mana. Then look at Chrono Trigger, even more different.

Chrono Trigger falls under the Turn Based RPG genre, which I would put under strategy. That is why it is different. See, there really isn't any consistency in Role Playing Games, that is why I consider them different genres. Also I think it is more of method of categorizing opposed to opinion.  If you use a taxonomy type of method that I use where you ask a broad question and answer it creating two different categories from that question, then it will work out my way. If you just list a whole bunch of characteristics and compare then it will not.

Hum based on your post you do have a point. I've always seen RPG as an conjuction of various sub-genres that made for the whole. Like Feylic said, each sub-genre is way different in it's core.

Zelda is different from Chrono Trigger, Diablo is different from Persona, Final Fantasy is different from Fallout and so on.

But take nowadays gaming standarts. Which genre is trully unique, in a way that it doesn't involve any other mechanic than it's core base in which that genre started? You have FPS's that use a leveling up system much like the RPG genre.
You have the adventure genre that mix more and more platforming and puzzle mechanics that were typical point-and-click genre oriented.
You have racing games that also use a leveling up system or mechanics that we're only found in prior MMORPG games.

Today, a genre is not defined as it was in previous genres. As games evolve, the boundaries between genres will dissolve even further.

Wow, Chrono Trigger a strategy game? Thats a new one. Well if you assume everything to be the way you think it's going to be...then things are probably going to turn out the way you think they will. It's not the fighting style that makes an rpg into an rpg, so turnbased rgps are still rpgs. Question? If you can use guns in strategy games, and you can have guns on cars in racing games, and you can have guns in fighting games, and you can have guns in fps, and tps, and you can use guns in rpg's, does that mean that all games are shooters?

Wait, Chrono Trigger as a strategy game? That's stretching the genres a bit too far. Have you played Shining Force, Fire Emblem, Yygdra Union, Riviera, FFT? What genre should you fit those. Do you think CT is even in the same gameplay frame as those games?

No of course they won't be shooters. Shooters are a sub-genre of Action games. You can't put a sub-genre into another sub-genre. Also if you didn't know all ready, I get irritated when people call Metroid Prime a shooter when in reality it is an Action-Adventure game. Also your metaphor has very little do with my method. I'm talking strictly gameplay, content has very little to do with what a genre is. Why would I classify a game by the weapons it has? Makes very little sense. What is a good way of classifying a game is how it plays. Chrono Trigger plays like a strategy game.

can we not pretend JRPG, WRPG is a genre & be happy?

what you have said now has confused me