how do you understand the songs if you dont know the storyline??
You don't need to understand the songs to listen to the music and be a fan. I listened to them before I knew the story and loved them just the same. Their music is fantastic, but I would agree that unless you know the story you just don't get the whole, amazing, experience.
I also saw them on tour with Blood Brothers, mewithoutYOU, and Dredg... Really wasn't a fan of the Blood Brothers, cant really remember mewithoutYOU so I'm guessing I found them average live, and Dredg was amazing.