I guess the distinction is more clear to me when you consider computer RPG's. What is the real difference between a 1st person shooter and an RPG? The extent to which the story is developed and the character makes life path altering decisions. The difference is not really achieved or expresesed by a player having a "colorful and interesting" character.
That's one difference.
The other is that the computer neither recognizes nor cares about anything but the mechanics. It only sees "fighter", and never sees the personality of the character. A living, breathing DM sees so much more than the machine ever can.
In a real RPG I'm not so concerned with kill ratios and where I'll find my next ammo pack.
You see, the 1st person shooter game has a set course, with set goals you need to achieve before you can exit the level. In RPGs we call that type of scenario a railroad, and most players I know hate them with a passion.
Based on your word choice and the examples you used, I infered that "roleplaying" is more about this concept of people adopting personalties like characters in a play. You talked about Igor Thud and how he can't be replaced because he is unique.
Not exactly. Igor could be a dime-a-dozen stereotype for all it matters in this discussion, with essentially nothing unique about him. But "fighter" isn't a plug-in replaceable part in a good game, any more than "Quarterback" is a plug-in replaceable part in a good football team.
Yeah, you need one, but which one?
A QB who's got a howitzer for an arm is a great asset, if he has receivers to throw to. If the rest of the team is geared towards the running game, that howitzer is going to sit silent most of the time.
So even in the pure mechanics view of the party, there are nuances to the classes, often expressed in the design of the character build, but even more often expressed at the tactical level in the decisions made during play. Does the fighter charge in to try and take out the enemy spell caster, or does he hold the line and defend his more breakable friends?
Does the cleric take a melee role, or is he more the "laser cleric" build, preferring ranged assault via his spell selection and use? Or maybe his name is "Medic", with the infamous red cross on a white field as his crest, and all he does is follow the big beef around and keep plugging hit points into him whenever he springs a leak.
I'm only comparing the combat facet of the games because the 1st person shooter game you compared D&D to has little else. Rather like viewing a NASCAR race strictly by looking at pit row. The race may be won or lost there, but if that's all you look at you're missing the best part.
I think that, over all, we have very different views of the game. You talk of the DM guiding you through their story. That sort of suggests that you're on a fixed path, and the DM will herd you back onto it if you make a wrong turn or miss a clue.
When I run an adventure, I have certain goals in mind for the party, but I'm also ready for them to side-track, or even get completely lost. I usually know what happens if they fail. It's more an exploration of the game world, with lots of choices and no fixed path or goal.
For example, our current campaign began with political troubles in the empire. The old emperor had been killed in battle, and there were three men trying to claim the throne. This was politics well above the pay grade of a bunch of first level types, and they had been advised to keep their heads down and stay out of that. Their goal was something completely different, to find an agent provocateur in the city. If they'd pursued that they would have discovered that he was selling secrets about the city's defenses to the barbarian hordes, and arranging assassinations of key people to weaken the city and prepare it for invasion.
By the party's decisions they ended up meeting this person, and getting manipulated by him into spreading chaos and inciting the already tense situation between the three emperors. They nearly started a civil war, in fact. That was a completely different story path and outcome than that particular story arc was set up for, but we took it and ran with it, and the consequences have had an impact on the entire campaign.
So, tell me which combination of classes and builds would have made a difference there?
<EDIT>I thought about this a bit after I posted, and realized that it might come across as "More story driven than thou". Sorry I offend, I didn't intend it that way.</EDIT>