can you prove this?
*farts at your direction*
I'ts actually a pretty good question. First of all, it should be clear that Nordic death/black metal scenes produced the most romantic metal yet expressed, as they took mythic imagination of metal music to a whole new level. The best of romantic metal:
At the Gates - The Red In The Skies Is Ours
Dismember - Like an Ever-Flowing Stream...
Therion - Beyond Sanctorum
Sacramentum - Far Away From The Sun
Mayhem - De Mysteriis Dom Sathanas
Bathory - Hammearheart/Twilight of the Gods
Darkthrone - Transilvanian Hunger
Emperor - In the Nightside Eclipse
Immortal - Pure Holocaust
Burzum* - Filosofem
* First four albums have nearly identical vision which gets more introverted and articulate with each succession.
Now, which of these albums is most encapsulating of other's varying moods and aspects?
I think we can safely exclude the death metal masterpieces, since their sheer energy isn't match for black metal's superior expressiveness in mood. "Transilvanian Hunger" and "Pure Holocaust" are too restricted in their aspiration of chilling rationalism. Likewise "Far Away From The Sun" and "De Mysteriis Dom Sathanas" are constrained by their efforts to reach most warlike and macabre art respectively, which leaves the final decision between Burzum, Bathory and Emperor.
It seems that the crypto-intellectual musings of Emperor and Bathory's apology of ancient living both find a common representation in the third work. Hence, Burzum's Filosofem is the epitome work, summary and ideal, of metal spirit. Subtlety of moods make it really powerful.
Note: this especially isn't saying that Filosofem (or Burzum in general) is the height of metal spirit, although close it may be.