Well it's what officially made me a Rugby fan. Simply.
I knew about the Wallabies, Boks, All Blacks...some french players throughout the years...some basic rules...guys like Wilko and Moody, Paul O'Connell, O'gara, BOD, Parisse, etc...and I'd watched some RWC and 6N matches til that point, coz my dad was a huge fan, but I was really an NBA fan. Knew about Toulouse and stuff...
I wasn't even aware it was the RWC, I log onto the news and see it's up. So I watched everything my TV showed, all of France's pool games etc...and for some reason I picked it up big at that moment. By coincidence, France went on to the Final, as if just for me in my little world so to speak.
A RWC is a gigantic promotion of the sport, no doubt. It's not just ppl saying this, it's a concrete reality.
There's the thrill of nations fighting it out (I wasn't interested in clubs until a few months after the 2011 RWC...), what's at stake in any World Cup of course - and you can take the time to inspect every part of the game all the same while. And the more you understand, the more you can enjoy, the more you want to watch, etc...it's a virtuous circle, and loyal fans are born.
Needless to say the 2012 6N, my first as officially a fan, was a GIGANTIC disappointment !