Opeth was fantastic! I really enjoyed their performance - very atmospheric, moody show, with a wide range of sounds/styles. Even my wife thought they were pretty good, and she wasn't sure what she was getting into for the night.
Mastodon was cool, but I'm not very familiar with their music, only have Crack the Skye. There were probably more Mastodon fans at the show than Opeth fans, despite Opeth being the headliner (at least here in Corpus). They had one or two more melodic songs, and the rest were very heavy/aggressive.
We missed Ghost unfortunately, got to the show late (after going fishing lol), so I have no idea how they are live.
I think you'll love the show, Shawn!