If a mainstream game needs to be known and played by non-gamers, then Nintendo almost have the monopoly on that one, with only Guitar Hero as their missing ace. I saw all three games advertised on the sides of buses at launch. As far as I'm concerned, advertising on the side of a bus is marking your game as mainstream.
Fun and interesting don't necessarily equal popularity, but for the most part they do. A good game with solid marketing will hit mainstream. Even an average game with excessive marketing or a fantastic game going by word of mouth can manage it, but a balance of good gaming with good marketing is the most successful formula. If your game doesn't make it to mainstream, you can wallow in pretentiousness, warm and secure in your belief that liking it somehow makes you better than the rest of the planet, but chances are, there's a better reason that people didn't pick it up than "Most people are too stupid to get this". When your game was advertised on the side of a bus, then the marketing wasn't the issue.