The old game is a different game than the new game. There's still dice and elf talking and a DM and so forth but the particulars of what constitutes table time and the emphasis of the rules on different activities will probably seem very strange to people who grew up with Pathfinder and White Wolf.
So how do I say that to people in a short, enticing way?
The first step towards understanding is to figure out what the right question to ask is. This is a big "DUH!" moment when you see it in the rear-view mirror, but it always surprises me each time that I realize it in different learning situations.
You see, I've been asking the wrong question, and of course then getting the wrong answer.
This is how I said it in the Foreword to Treasure Hunters Prolix:
This is not a game of skirmish & volley! This is a game about Exploration, Acquisition, and Reclamation first and foremost; and about the heroes who undertake these challenges.
Occasionally there is no alternative but to skirmish, so rules for skirmish are included. But make no mistake: this is not “Fantasy Street Fighter II”; this is “Fantasy Oregon Trail.”
This is most jarring to those who come to RPGs through those composed the modern way. "When do we get to the good stuff?" asks the modern edition gamer, because to the modern eye, the game "should" focus on tactical simulation. Often table time is dominated by skirmish, which puts the squeeze on all the rest of the game. This is by the design in the modern game: over time, the game genre has evolved to emphasize and reward this kind of play.
The older game is a game of resource management. The heroes have scarce resources: game turns, Hit Points, rations, torches, &c. The player is to manage these and turn them into other resources: gold, personal power (experience points), and in-game knowledge, thereby growing the hero's ability to manage the former through application of the latter.
The several players should make their heroes to be self-directed within the game world the Referee provides. In setting goals, overcoming obstacles, and reaching those goals do the characters grow, & Adventures surely will transpire.
This is long (prolix) and certainly not how I would say it, face to face, to another human being. These words do not roll off the tongue! So how do I say it?