What makes the essence of a game?

[bluestarultor]

So, trying this again, what makes the proverbial "atom" of a game per genre? How much can you strip out and still have it be a game of that genre? The idea here is kind of like when Yahtzee said if you have a good zombie movie, you could strip out the zombies and replace them with koalas and it would still be a zombie movie. How far can you boil a game down and still capture its essence?


Edit: I guess I'll start off. I, as indicated, think it depends on the genre. Just a few examples, but for an RPG, you need characters, a story, and some sort of atmosphere, be it focused on music or graphics or both. Combat, in my opinion, is completely optional, because the story is at the heart. Good combat helps, mind you, but you could theoretically do without it. On the other hand, others are nearly boiled down to basics as they are. Fighting games started modestly and could function modestly. All you need are two sprites of different colors that punch and kick and off you go. Anything on top of that these days boils down to pretty graphics and sound and more interesting ways to punch and kick. Nothing against fighting games, because I like them and there are some good ones, but they're still pretty simple.