Bluesky, before I got into Katatonia, I was always a fan of gregorian monk chant (in fact I'd love to hear Katatonia do some songs with that in the background). I love the subtle changes in notes while being sung in a brooding, despair-filled tone (although in gregorian chant it is done slower). He does it in older songs (like "Passing Bird") but the burdened tone in his voice is missing. The tone of Jonas's voice now is what makes it work so well. For example just using "My Twin" as an example....the parts that make the whole difference in that song is how he sings certain words in the verses which are in bold:
"
I thought that you had grown, that you would carry on. But now that I am gone, what else has been withdrawn?"...the way his vocals carry up and then back down (very subtle) on the words "grown" and "gone" is what I love to hear and what gave me chills the first time I heard it. For me it's not about the range of his voice or whether he can do falsetto. I love the subdued, tortured, "sick to death of life" type tone in his voice nowadays, and when he adds that very subtle melisma to his voice, it adds a haunting beauty to such a tormented voice. He does the same thing in other songs like "July", "Departer", etc.
The music itself was always great in Katatonia, but I couldn't hear that controlled melodic misery in his voice in their earlier material. It sounds (as you described) "flawed" and raw, almost like he recorded the vocals up in his room (although there are songs like "Omerta" and "A Premonition" where it sounds better than others). A lot of people can appreciate that raw sound, but for some reason it doesn't sound near as dark/eerie to me as what he does now. I love to hear a haunting melodic voice fronting dark, brooding music. I love the band Tool for the same reason as Katatonia (although Maynard does have more range with his voice and it does sound controlled, whereas Jonas has to try a little harder to pull in those few wild horses, which is why I don't think his voice works as well when he uses more range).
I would love to hear some of their older songs rerecorded with his newer style as I am certain I would like them better that way. "Dispossession" is just one example. I absolutely love the music in this song and there are parts where I enjoy his voice, but there are other parts that make me cringe. There are no "cringe-worthy" areas to be found anywhere on THE GREAT COLD DISTANCE nor NIGHT IS THE NEW DAY (except for when Jonas disappears in "Departer" and Krister takes over). The only song from either two albums where he sounds different (vocally) is "Dissolving Bonds". He sings the verses in a different tone than the rest of the newer material (the first time I heard it I actually thought he sounded a bit like Dave Matthews), but it still works in this particular song, especially back at the chorus.
Anyway that is the best way I can describe it with my limited technical knowledge/vocabulary when it comes to the actual music-creating process. I know what I love to hear and can instantly recognize it when I do hear it, but I am very bad at describing it properly.