I was thinking about this the other day wanted to capture the thoughts. For about any Role Playing Game there is are 3 fundamental styles that give and take in a 3-way triangle in much the same was at Cost <-> Quality <-> Time. For an RPG these elements are Roleplay <-> Simulation <-> Game. These 3 elements exist to some degree in each RPG, but can be seen more clearly in extreme examples. But first a quick definition of what I mean.
Roleplay: This is the aspect of the game that is not a game. The desire of a participant to act out a role. No mechanics are necessary for roleplay--you just make it up based on your idea of the character and the world.
Simulation: This the degree that the RPG attempts to model reality. While all RPG's are fictional, some try very hard to model real-world physics and other real features. RPG's with a strong emphasis on simulation are usually modern military type games, but even pure fantasy games like Dungeons & Dragons attempt to simulate physical combat with complex systems design to estimate chances of success and resulting injuries.
Game: This is like Simulation, but not so much. This is the aspect of an RPG that is not based on reality and makes the RPG play more like a game and less a simulation or a roleplay action. An extreme example is chess. In chess each player is controlling a king's army, but each piece must follow rigid rules about how it moves on a grid. This does not simulate reality in any way and there is no emphasis on playing in character (roleplay).
All 3 elements combine to create a variety of RPG experiences from very rules light (tending to be strong roleplaying) to very rules heavy (tending to be miniature based combat simulations). Whether any particular game is enjoyable will depend entirely on the player's preferences.
I liked the idea of the 3 elements because I think it might be useful in describing games to other potential players. Personally, I like a game with more roleplay and game and less simulation. So if I were reading a review of a game that was rated 10 for Simulation, I might infer that game was designed for a different kind of player.
Nothing all that profound... Just random musing.