The one thing I think is most important when it comes to roleplaying in video games, is choice.
The more choices, the larger the room for roleplaying. Take Call of Duty's singleplayer campaign. You can roleplay - albeit minimally. The only real choice you have is what weapon to use, and it's of course limited to what weapons you find. Does your Jackson prefer shotguns when in war? Does your Roach perhaps use pistols as much as possible because he likes small and light weapons? I'm not saying that CoD is an RPG, I'm not even saying that choosing weapons can be labeled as "RPG elements", but you can roleplay. All games are limited in choices, where corridor shooters like CoD perhaps have the most limitations.
I roleplay in Jedi Academy. Once again, there's not enough choices to call it an RPG, but towards the end the choices are large enough to be labeled as RPG elements IMO.
Over the course of the game, you can choose your Force powers. In one playthrough, I only used dark side powers and slaughtered every enemy I saw, sometimes cruelly dangling them over drops before letting them fall to their death. I used my lightsaber most of the time but used ranged weapons sometimes. I used a doublebladed lightsaber because my character thought it was the fastest and most effective way to kill my enemies with. Towards the end I picked the evil ending.
In my other playthrough, I only used light side powers. I tried to force pull the weapons out of most of my enemies hands and spare them. I only used my lightsaber. I picked two lightsabers because my character thought that it was the best choice of weapon to defend with. Towards the end, I picked the good ending.
There wasn't that much to choose from, but I did roleplay with the choices I had.
In a real RPG as Oblivion or KotOR, there's choices everywhere.
In KotOR you can choose your response in every dialogue. You can choose what you and your party members should wear and wield, and what stats they should have (what they are good at).
Sometimes the dialogue choices have more repercussions than a different answer, like how a quest ends.
In Oblivion there's less dialogue choices, but instead you can choose where to go, what do do, anytime. As it is an open-world sandbox, you can choose to fish for scales and pearls in the Rumare, then hire a room in Pell's Gate. You can steal a horse and go to Bravil and sell the pearls there. Or you could buy the horse and go to Skingrad and stalk Lazare Milvan. Perhaps join the Fighters Guild? Or screw the pearls, why not rob Countess Umbranox and join the Thieves Guld, selling the jewellery to Ongar? Or play as a law-abiding dungeon-crawler who only explores caves because forts and Ayleid ruins scare him (because of a hideous event that transpired when he was a child, and therefore he will try to extract revenge on his childhood demon, which is http://www.uesp.net/wiki/Oblivion:Jalbert).
I got a bit carried away, but my point is that, mostly because of the open world, there's so many choices in TES that you can build a roleplaying story like no other - and I haven't even mentioned your stats and equipment, which are just as diverse as KotOR's.
I think that BioWare games are more epic and "tight" than TES games, but in TES the epicness is more spread out over the game world, and with all the content and the freedom the game length is a lot longer, and your roleplaying choices are even more. :tes:
And again a choice without a meaningful consequence is not really a choice at all, it's just an illusion of choice.
I agree... to an extent. Remember that a lot of the role-playing experience comes from yourself, from what you imagine and then project onto the game.
A conversation in KotOR can have 3 dialogue choices, where two of them, while different, can lead to the same answer. The result of the conversation will be the same, and you get no different remarks from party members or anything. But if one choice was rude while the other one was polite, you are still defining your character even if nothing in the game reflects this. It's like walking instead of running inside cities in Oblivion - NPC's does not care whatever you do, but you may decide that your character doesn't want to disgrace her/himself by running inside a bookstore.