Vestin: Having evolved from table top
storytelling games, the RPGs' heritage is that of plot-heavy drama and deep immersion. Their single greatest goal is to offer a chance to temporarily
be someone else, shattering the player-character relation and instead creating unity.
Be someone else? Overall I find that PS:T has rather poor writing compared to many books I've read. That coupled with generally poor overall gameplay makes it a poor game. Arcanum does at least have a somewhat decent gameplay, and the writing isn't as bad. When a game gets stuffed so much with text, the quality will fall, making it very hard to "be" someone else.
Vestin: If we are to hold that a game like Diablo 2 is an RPG, we would have to either admit that the core philosophy behind the genre is not as evident here or point at tabletop D&D as an inspiration. Well - that and LARPs like SOLAR, where people run around and beat each other with fake padded swords
Diablo 2 is an ARPG, Action RPG. It's based around stat heavy combat. It requires a lot more thinking than any "text based" RPG's, as you have to think builds and such through. That said, it's not about the storytelling, but the character progression through character enhancement. When you said "be someone else" I almost got this picture of a theater play, where the actors were given several sets of dialog, and would pick this and that based on what the other chose to do. Imagine that: "Live Dialog Role Playing".
Vestin: IMO - an RPG should be even more about story than an adventure game. We should never just assume that "if it has a stats and/or a character sheet - it's and RPG". Also - the story should NOT be linear. The player should be able to solve problems in many ways, go wherever he wants (and can), etc. Choices, freedom, lots of dialogs, immersion and - yes - character development (usually using a character sheet). That's what makes and RPG.
The core philosophy between tabletop storytelling based games, and a computer RPG's are two
wildly different things. Choice and freedom are wonderful things, and are also evident in several combat based RPG's. Lots of dialog is OK, if done correctly. Fallout, Baldur's Gate and such, had lots of great dialog, but it didn't depend on it. And since it wasn't dependent on it, they could think things a lot more through, making the games overall a lot better. Immersion is up to each individual. I don't find much immersion is PS:T because I find it to be so poorly written. Arcanum is a lot more immersive, even though it suffers from a lot drawbacks as well.
Titan Quest, Sacred, and as you mentioned; DIablo 2, are so called ARPG's. Real time at that. They are based in stat heavy combat, and have little choice or dialog, because they are based entirely in the action. Hence the term "
Action RPG". However there is a difference between that and games like Temple of Elemental Evil and the SSI Goldbox games. Those games have story, dialog, choice and consequence, but are still stat heavy and for the most part combat based, which most CRPG's are. Though with games like Fallout you can chose to not engage in any combat, but I find it to just get tedious to take the pacifist route. Especially if you happen to get into a combat situation where you just have to run.