Saw R.E.M. in 2008. They were great, but Modest Mouse opened for them. I'd heard, like, maybe two Modest Mouse songs before that point, and my impression was basically "they seem alright."
Jesus they were bad live. Ended every song just flailing tunelessly on their instruments for a minute and a half. You can end, like, one song that way per set. You don't want it to be your thing.