I understand the hesitation. I was the same way when I first heard about it, and it took me a while to even try it.

The actual explanation is only a few minutes long. The rest is just other questions about the game, and about him.

The Wikipedia page has a good introduction paragraph that explains the game quite accurately.

As far as its popularity, I'd say it's done incredibly well being that it is just an indie game by a single developer with no advertising beyond word of mouth from the players.

As of October 2nd 2010, Minecraft surpassed 1,000,000 registered users and 300,000 purchases.