ISIS requires little in the way of introduction. Hell, along with Neurosis, these guys are a buzzword incarnate—few bands have spawned such an enormous pool of imitators. But despite their ubiquitous and seemingly permanent association with the current crop of build/crescendo/repeat post-metallers, ISIS have actually undergone quite a series of stylistic transformations. Though they will always be remembered for Celestial and Oceanic, Aaron Turner and company have evolved from sludgy hardcore to post-metal to pensive prog-rock on 2006’s In the Absence of Truth. Consequentially, ISIS have both exploded in popularity—in part thanks to their tour with Tool—and suffered a great deal of I-liked-their-older-stuff-more-ism from their core fanbase. Before Wavering Radiant hit the streets, rumors swirled that ISIS were planning a return to their quintessential form—a grittier, less-artsy beast than we’ve seen for the last few years.

And for the first few minutes of opener “Hall of the Dead,” it sounds like ISIS really have taken a step back in time. Though their recent aesthetic remains largely intact—keyboards and serpentine, organic rhythms—its chunky, grinding main riff and Turner’s bellowed vocals could be straight off of Oceanic.. The band as a whole sounds more aggressive than they have as of late, thanks in large part to the work of new producer Joe Barresi. Barresi, who has worked with such noisy luminaries as Melvins and The Jesus Lizard, gives plenty of room for ISIS’s more delicate clean sections, but his production really shines in their heavier moments. Throughout Wavering Radiant, there are moments—like the swan-diving guitar crescendo in “Stone to Wake a Serpent” and the thundering double kick beats in “20 Minutes / 40 Years”—when it feels like ISIS are trying to retrench their appeal amongst their older fans.

But such moments are few and far between, and for the most part, this album stays the course set by its predecessor. Throughout Wavering Radiant, ISIS weave undulating prog-rock tapestries with an ambient bent and a hearty respect for Tool’s circular rhythms. The band’s ethereal quiet parts remain detailed and pleasant to the ear, with Turner and Mike Gallagher’s guitars chiming beautifully over drummer Aaron Harris’s complex-yet-unobtrusive backbeats. While their heavier moments enjoy a boost from the Barresi production, they fall short of the epic weight associated with Neurosis, Cult of Luna, or even many of their imitators. By and large, the louder parts of this album seem to exist as foils for the quieter ones, rather than as conclusions to lengthy, dramatic buildups. So too does Aaron Turner’s voice function. His vocal contributions are the weak link in ISIS, and he wisely chooses to relegate them to a decorative rather than central role in his songwriting.

Sometimes the formula works splendidly, as on “Hall of the Dead,” “Ghost Key” and the surprisingly aggressive “Threshold of Transformation.” Sometimes it doesn’t; “Hand of the Host” is overlong and under-wrought. Throughout Wavering Radiant, though, it’s hard to escape the feeling that ISIS have finally begun treading water. Nary a forward step is to be found on this album, and more importantly, it doesn’t actively seize the listener’s attention, and that’s a problem for any band, no matter how atmospheric. Wavering Radiant is a meticulously-crafted album that has plenty to offer the established ISIS fan, but those (like me) hoping for another step along the evolutionary path may be disappointed.