(Originally posted on EN World, but re-posted here since people on that site seemed to like it.)
I think you can learn a lot about a game by listening to how people describe it after they play it. It shows you how they interact with, see, and process the game.
For instance, last weekend I played Carcassonne. I had some lucky draws I was able to exploit by managing my meeples well. I was able to keep churning through cities and roads, completing stuff at a steady enough pace that I was able to drop some farmers early without hurting myself in the late game. My opponent built a couple of huge cities to narrow my lead, but my edge in farmers sealed the game.
Compare that to a description of our lunchtime Keep on the Borderlands game from Tuesday. The characters had been ambushed by wererats at the Stumbling Giant (the tavern in the keep) the session before. With the help of the guards, they figured out that the wererats posed as halfling merchants and had visited the keep several times before. Oddly enough, though the guards at the gate reported that the halflings always left with a heavily laden wagon, the gnomes they traded with never sold them all that much copper and silver ore. The gnomes were surprised at the guards' description of the loaded wagon.
The PCs had arranged a meeting with the keep's ruler. Unknown to them, the ruler's trusted advisor disguised himself and sought out the PCs to question them. Faced with an inquisitive stranger, the party's wizard slashed the man's arm with a knife to see if the non-silver blade would deal any lasted damage.
It did, and the session ended with the characters entered the ruler's audience chamber to find the "wandering tracker" they had harassed standing at his side.
If you look at my second description, I think it's something you find for most RPGs and other immersive games. I'd describe playing Mass Effect in a similar manner. There's something very important there, a mode of thinking and experiencing the game that the mechanics should support. It's definitely something that influences the Essentials process and a lot of my design.
It's something that I think of as the game's metaphor, or its idiom. To an outsider, D&D is a few people sitting around a table, rolling dice, consulting books, speaking in funny voices, and maybe pushing miniatures around a grid. To the people in the game, it's a tense expedition into an ancient ruin, made all the more deadly by the bloodthirsty, recently awakened vampire that stalks the tombs they explore. That's an important part of the game. Without it, the game is little more than what it appears to be on the surface.