They are a fantastic band with the screams or growls or "death vocals". It adds to the flavor of the music. Prog to me is a musical journey, and Opeth have decided to take that journey. The "death vocals" only add a different dimension and character to the music. The great contrast between the screams (Some of the most tortured and intense, not like the barking of some sh*te Death Metal acts) and his "regular" (And very pleasant sounding voice) is incredible and makes the music more compelling. Very few bands who do the screams and singing also can do both well, or with conviction. Without either one, they just wouldn't be the same, and if he ever decided he was bored with one or the other, I hope he changes the name of the band.
Anyway, the interviews I've seen lead me to believe he has no intention of getting rid of them anyway...
This will probably kill any cred I really don't have anyway, but as far as separating the line between music and noise, well, I love harsh noise/experimental, too...so there you go...