I won't be shocked if Mastodon wins or doesn't win. The reception on The Hunter hasn't been as strong as it was for Crack The Skye, but it has gotten a strong enough reaction to make a run for the top spot. Like I said the other day in the Now Playing thread, there are so many albums (from just about every subgenre of metal) that have gotten an extremely postive reception this year that it's going to be really hard to predict what albums will finish in the Top 10. If I was a gambler, I would say Symphony X, Mastodon, Opeth(though it won't finish as high as past Opeth albums have), and Vektor are the only locks for the Top 10 this year.
6/21 Fall Out Boy