Opeth has undergone yet another metamorphosis.

The Swedish band was already a unique metal outfit in 1995, when it released its first album, "Orchid," a collection of songs which blend heavy riffs, primal-scream vocals and elements of folk and prog. Twenty-one years later, Opeth still embraces that experimental approach on its 12th album, "Sorceress" -- just don't expect it to sound the same as the old stuff.

"Sorceress"...