>>724583594
I think of Role Playing games as games focused mostly on making a character that is very unique to you. Meaning you choose your race, class, stats, etc., and the game is open in the way it reacts to your choices. Most of your choices are made in menus and dialogue windows. There is an undercurrent of D&D dice rolls behind the game as well that make RPG's unique from action games.
An immersive sim, to me, is more about making choices within the game world, and those choices are made through actual input actions and real time gameplay. The immersive sim, probably started with Ultima Underworld and System Shock, is clearly an offshoot of the RPG... but it has a more action driven, real time bend to it.
Ultimately it's semantics. I love how much interactivity and reactivity there is in Gothic and how the world feels alive and in motion on its own.