I've been to a fair amount of live shows and I can say that without a doubt everything about sigur ros stepped up "indie" shows about a million clicks. I was in awe all night long. I had the pleasure of seeing them about 2 years ago, so I can only imagine how much better they are now.
The music and the live sound were both amazing, they travelled with their own PA when I saw them, which made a world of difference. I love how you can just tell that music is their life, and they take it so seriously. I agree with J. if they are ever in your city do WHATEVER you can to make it to the show.