now, i personally don't like opera in combination with metal, like nightwish and within temptation or whatever, but therion is totally ok when it comes to that combination, becouse it sounds very powerfull...
maby you need some time to like it
try with "lepacca kliffoth" and "theli"...can't go wrong i think
I dated a girl who was obsessed with them. She had something like 25 t-shirts, 10 of which being homemade. She's going to wacken this year just so that she can see them.