Although Isis' riff-heavy approach to post-hardcore has won them acclaim among sludge-rock enthusiasts, in reality the band's arrangement-rich approach is light years beyond the heavy metal ghetto they risk being cast into. With "Oceanic," the Boston group has pushed their boundaries even further, simply using heavy chords and frantic screaming as a point of departure for experimentations that alternate between dense complexity and ethereal dreaminess. Sure, there's riffs, and sure they're heavy. But Isis incorporates modalities and tonal colors in these "songs" that rival the playbook of most head-up-ass modern composers. No, it's not brainy, and no, it's not overly obscure. But a track like "Carry" can build from delicately flavored, feedback-drenched atmospherics into a full-bore metallic assault -- and it's the atmospherics that are the true focal point of the track -- and "Maritime" does little else but evoke a tiny little boat in a very big sea. It's not lunkhead aggro-rock we're talking about here. It could be said that "Oceanic" is the defining moment of Isis' career, but in reality, it's clear that this band has many more ideas to explore.