They would fare better if they played some more old material but, and I'm a huge Mastodon fan, they really are a band that are much more fitted to a club-sized venue. I just can't imagine their music translating well in a big amphitheater in the middle of the day or whatever.
5/4 - Rob Zombie?
5/11 - Ghost
5/13 - Mastodon / Gojira
5/21 - Primus
6/28 - Iron Maiden / Ghost - Bergen, Norway