Preposterous as the concept of "commercial" black metal may seem, Norway's Keep of Kalessin have come to epitomize just that, as they've steadily discarded their more savage tendencies on each sequential release leading up to their fourth full album, 2008's Kolossus.

Even more so than its already quite refined predecessor, Armada, Kolossus is characterized by crystal clear production, aggressive but disciplined performances, and unflinching (if hardly outlandish) stylistic deviation from the genre's more conservative trappings -- all this without mentioning the quartet's corpse-makeup-free, Elven good looks.

Oops, we mentioned it.

Anyway, since KoK was never the most stable of bands, it's also notable that ever-present guitarist Obsidian Claw finally managed to retain the same lineup for the three-year span between these two albums, and the fluidity of Kolossus' material shows they've really had a chance to gel as a recording unit because of it.

This material ranges in length and variety to take in both straightforward numbers like "A New Empire's Birth" and "Ascendant," and elaborate excursions into compound moods and tempos like "Against the Gods" and "Escape the Union." Yet all of them invariably find a great balance between wholesale riff mongering and melodic sensibilities of the highest order, whether flirting with Darkthrone or Satyricon's back-to-basics approach on the rock-infused "Warmonger," or encroaching upon the synth-enhanced realms of Dimmu Borgir and Cradle of Filth on the gothic "The Mark of Power." Obsidian also hoists his acoustic guitar with confidence and authority on several tunes, including mold-breaking opener "Origin" and the, erm, "kolossal" title track's Spanish-flavored midsection.

Then he mixes it with some impressive piano playing for "The Rising Sign," which, ironically, only threatens to implode during its frenzied, blastbeat sections -- not the softer parts.

For his part, vocalist Thebon draws the line at venturing into outright clean-singing territory (although he'll probably try that next!) by retaining his rasps at all times here; but he shows no qualms about alternating his typically hoarse black metal vocals with portions of quasi-hardcore shouting, and deeper death metal growls -- surely opening the dungeon doors for some amount of intra-genre bickering.

All of it pointless and counter-productive, of course, given all of the creative back-and-forth -- most of it refreshing -- between these long-standing bastions of musical extremity.

And even though a few detractors would certainly cite such matters as further proof of Keep of Kalessin's betrayal of black metal's true kvult traditions, most unbiased listeners simply looking for good music will surely be impressed with what is arguably the band's best album yet.