More intelligent discussion of music and less undergrad masturbation about the nature of the universe, please.
OK, let's seek out the nexus between the two subjects: the best albums of metal have expressed some aspect of potentiality--that is, the ability to generate content that provide cues for future artistis within the genre (or formulators of an entirely new genre)--whilst bands that create "dead-ends", which may appear as competent, thoughtful albums at the time, nevertheless pale in comparison. This is the difference between "Hell Awaits" and "South of Heaven". Another example of this would be Demilich's "Nespithe" vs. Emperor's "In The Nightside Eclipse". Though no band claiming to be directly-influenced by the former has emerged, or produced a worthwhile release, "Nespithe" remains a benchmark to entice intelligent, creative musicians to one-up this masterwork. Meanwhile, ITNE generated an indefinite amount of rip-off bands that capitalized on the use of cheesy synths and melodramatic riffing.
How does this relate to the previous posts? From the very origin of music, there hasn't been any significant increase in quality of the artform. Rather, that which has persisted has done so because of a trans- or supra-temporal character that nevertheless blossoms at the appropriate age, and suffuses its audience with information pertinent to their growth (or survival!).
Therefore, the best music is that which works with the most comprehensive set. In effect, it comforms most closely to some aspect of the universe (or cosmos, which might be the proper term here--there isn't really a need to isolate space from time, because the two are inseparable insofar as they are jointly embedded in the physical condition).
The best metal in subsequent years will be that which will exemplify the mathematic principles inherent in the artform. Fuck Romanticism...the fugal form of the Baroque is absolutely essential to the survival of the genre. A shift in this direction, both by the demands of the listeners as well as bands, will ultimately distinguish the transient garbage from the truly potent material. Otherwise, people will continue to seek novelty and find merit in blithe attempts at self-expression. Nature doesn't merely consist of a radiant forest withdrawing its thorny boughsfrom the well-wishing ambitious traveler. Nature will fuck you up and leave even the most sincere environmentalist for dead, not because it concerns itself with the morbid, but quite simply because it is governed by fixed laws. To that extent, the best of metal must convey this--and that is why black metal, brimming with suburbanites filled with a sort of refracted ressentiment, will ultimately fail to yield any worthwhile progenitors of metal to come.