I was also finicky about such things, but if you stick with it long enough, the vocals will "fade" into the background. So, in a sense, DL does have a point, but when all factors work together to create a whole, then in the final analysis no single factor can ruin the whole, either. So the "problem" kind of is "with the listener" at this point. That article by Aaron Copland that was linked here a few weeks ago about the 3 levels of understanding and appreciating music comes to mind.
But let's be clear, lyrics are not the same as vocals. And I take exception, NHA, to you saying that metal lyrics tend to be garbage. Not the metal I listen to. Yes, it is not particularly sophisticated; it is, indeed, primitive, but therein lies its charm! In fact, the more that metal lyrics tend toward sophistication the more they fail miserably at it. The more primitive-minded, the better. Graveland and Immortal come to mind as personal favorites. Have you read the Sagas? Are you familiar with the literary technique of the kenning
? Immortal's lyrics are very kenning-like!
A third factor that should be considered is neither how the vocals sound, nor the meaning of the lyrics, but HOW the vocals "interact" with the music. This dynamic is one of my favorite aspects of metal, and when done well makes songs very memorable. What I am talking about is basically when the music "takes a step back" and the vocals "take a step forward." The song Thousand Swords on Thousand Swords uses this to great effect - after the first minute or so there is a perfectly timed groan brought to the foreground as the music almost "stops." The same goes for the "epilogue" of that song, as Darken switches to a more spoken cadence in the foreground - good lyrics to this song as well. Another one that comes to mind is Immortal "Unholy Forces of Evil." This is on Diabolical Fullmoon but the really good version is on the EP. It's at the part where the lyrics go "Sacrifices as old as the earth..." Notice how the music almost "stops" and the vocals become more "spoken." A thrilling effect!