What bands do you think shouldn't've gone mainstream? I'll start off with...: Metallica. They were doing okayish, even after Cliff's death, but when they made the Black Album, I was kinda disappointed. To see the thrash/heavy metal Metallica die, made me hate the "new" Metallica. They were no longer metal, but merely hard rock. If I had a choice to change Metallica when they were heavy metal, I would've kept them that way. Oh, but no. Metallica wanted more and more money and so they gave up the worst thing that they could've given up: Their heavy sound. Okay, your turn. GO!