I know that some people here like to use various metrics and classifications for digesting their (and others) designs, so I thought I'd pass this along.
The 400 Project is a growing list of "rules to consider about game design" being put together by some video game guys. The number 400 is purely a random number just to have a target goal.
While there is some amount "video game"-centric rules, there are quite a bit of general, higher level game design concepts at play also, that can be looked at and considered.
It can't be that hard. I'm sure they aren't interested the nuances or a rules explanation, just a basic idea of what the game is. In it's most simplest form...
"Puerto Rico is a game where you build a plantation, grow and harvest goods, and then ship them for points, or sell them for money."
Additionally, you could add "You spend money to buy buildings which give you special bonuses throughout the game."
There's no need to go into the whole "choose your role" thing, as that's not really what the game is about; even though it's a primary focal point of the rules and how the game works.