Based on only samples I haven't bought any Mastadon in the past, I think it is the vocals. The Hunter is quite a departure from their earlier stuff, not only clean vocals but shorter songs, not as Prog. I did buy this album though and like it a lot. One of the things I like other than it really Rocks is the songs don't sound the same. Some are high energy, a couple sort of droan, one I'd even call a power ballad of sorts, I really get lost in the last track. It would be cool on the next album to keep with this style but go back to adding some extended Prog tracks. I don't see how something off this album couldn't get the band some airplay. I can see several tracks being added to my mp3. I can't fault the band for following suit with bands like Slipknot who have tightened up production to gain more mass appeal.