My knowledge of musical theory is extremely limited, so this may come off as a bunch of non-sense, but I think I'm onto something.
One aspect of many early black metal releases that I have not found in recent releases is the presence of brief, semi-ambient tracks that usually explore a central theme with minor variations, explorations, and developments on that theme, while always returning to it, sometimes with a new realization or take on it. You might call them interludes, but that isn't quite adequate. Where most quality metal plays out like a journey, or a story, and most shit metal is a disorganized mess, these tracks feel more like musical poems. They serve not as an adventure for the mind and spirit, but rather a period of quiet contemplation after the adventure (or between adventures), where the logical and rational mind attempts to frame the experience of the adventure into a unified whole within the spirit and mind. It seeks understanding from the experience.
Three of the strongest examples of this "metal poem" are many of Burzum's works (The Crying Orc, Naar Himmelen Klarner, much of Hliðskjálf, Decripitude I and II, etc), Xibalba - Carchah (this track feels very influenced by the aforementioned Burzum songs), and Isengard - In The Halls And Chambers Of Stardust The Crystallic Heavens Open.
Other bands that make a lesser use of these techniques: Summoning, I Shalt Become, Beherit, Gorgoroth (Sorg).
Am I totally off, or has anyone else noticed this use of song construction? If so, what are some other notable songs in this style?