Dark, yes; morose, no. Hotter possessed a very rare voice; a genuine bass-baritone. Darker than a lyric baritone, not as heavy as a true bass and with remarkable flexibility and control, especially in fast or intricate passages and in the higher register. Compare as well his performance of Bach's "Ich habe genug" (currently available as an MP3 dowload for pennies). Moore, of course, was the preeminent accompanist of his generation, as he yet again demonstrates in this performance.
The dark timbre of Hotter's voice, where he often gives the impression of singing far lower than he actually is, almost succeeds in disguising some intensely subtle singing. For example, his is the only reading of this work that I know (among a dozen or more) that does not take the high notes in "Irrlicht" forte. The melodic line invites this, and no other singer, not even Fischer-Dieskau, seems able to resist the temptation to indulge his top notes here. Yet the harmonic argument clearly calls for a much lighter treatment of these high notes. They are grace notes, and need to be touched rather than hammered. Hotter and Moore also take "Letzte Hoffnung" extremely slowly; slower even than the Fischer-Dieskau/Jörg Demus version. This too has much musical logic, and allows both performers to explore the far corners of this eccentric and intricate song. Again, Hotter resists the temptation to bellow the final "cry! cry!", opting instead for the finest of decrescendi into a beautiful pianissimo. When he does choose to unleash the full power of his voice, as for example in "Auf dem Flusse" or "Die Krähe", it is easy to understand why he was one of the all-time great Wagnerians.
The other striking characteristic of this recording is the way the performers achieve a rare (unique?) balancing act between intense subjectivity and cool objectivity: sometimes moving seamlessly between the two; sometimes somewhere else altogether. Fischer-Dieskau, for example, was always deeply and irrevocably rooted in the Romantic vision, and seemed neither able nor willing to separate himself from the personal trials of the narrator. While he is the uncontested master in this genre and is unfailingly insightful, inspiring and exciting, I have never sensed the least detachment or irony in any of his recordings of this work with which I am familiar. Singers like Pears or Schreier, on the other hand, seemed much more comfortable keeping the mystery narrator at arm's length, strenuously avoiding getting sucked into the Romantic vortex. Still others, like Prégardien and Bostridge, apparently prefer using the work as a stage on which to express themselves first and the music second. Whatever the permutations and combinations, this recording is a work of supreme musicianship, subtlety and intelligence.
So do not be misled by Hotter's dark, brooding tone. That is in the nature of the bass-baritone voice. At least, his bass-baritone voice. Enjoy instead the challenging, possibly unique and endlessly satisfying musical insights that he and Moore uncovered in the course of preparing this performance. 50-odd years old it may be, but we may have to wait another 50 years before anything of this perception and quality comes along again.