I saw that Mastodon / Opeth show. Went mainly for Mastodon, I own a couple Opeth albums but wouldn't call myself a fan. Mastodon was good as always, but Opeth blew me away. They were touring their super mellow Heritage album so I was expecting a lot of people in the crowd to be yelling at them to play their older, heavy ****. But the dude had the crowd spellbound with the beautiful and haunting new material, cranking up the tension and expectation ... and then, towards the end of the show when he did get around to playing some old favorites, the place went absolutely bananas. One of the best metal shows I've ever seen. Hell, one of the best shows period.
Still not a fan of Opeth's recordings, for some reason they don't satisfy, but I'd definitely go see them live again.