I like to learn the rules first. If the setting is pervasive enough to require special rules, then I want a brief description, otherwise, just the facts.
Like Wombat, I judge based on character creation. That's my first goal, create a character. I don't plan on playing the character, but creating one helps me understand what's happening. Sometimes, I don't even write the character down, tracking numbers in my head, but the process is still there.