The very first time I heard them was Colony of Birchman, and I wasn't impressed. That album was too proggy for me.i did not really like mastodon at first. then Crack the Skye came out and changed everything. After that i ended up appreciating the older stuff more. i like all their albums but once more around the sun is kind of weak. Emperor of Sand was by far my favorite album of 2017.
the thing about them is there is no BS and no egos, no clichés. I liken them to a modern version of Rush in how they ineract with each other and the public. they seem like good people that are inspired to write music for the fun of it compared to a band like Electric Wizard who seem to half-ass a new album when they need attention.
Later I listened to Crack the Skye and I "got it." I don't love every song since, but I respect them and what they are trying to do. Are they a little bit of a gateway band now? Maybe. They are still much heavier than the "pop radio rock" moniker I've seen trv cvlt metal gatekeepers slam them with. There is nothing wrong with a little song structure, a memorable chorus, or dynamics.

