There's no doubt about it - growling is not for the faint of heart. However, in music like Opeth / My Dying Bride / some Katatonia it's just perfectly suited to display the kind of emotions involved.
As far as Opeth go, Blackwater Park is the most commercial sounding / ear friendly album they have released imho. The growls on that record as far easier for a new fan to take because of the higher amount of clean vocals / light tones that this album has. Blackwater Park, with the exclusion of Damnation, is probably the lightest record that Opeth have made.
On the other end of the scale, the most brutal of growling exhibitions from Mike would be found on My Arms Your Hearse (he had a cold on this record, so he seems to have a deeper growl imho). Closely tying (in terms of growling), would be Deliverance. I think (despite the album being a slight step back muscially), the growling on this record shows Mike being more diverse with how he growls and shows him being the absolute master of this art.
The first two Opeth records, Orchid and Morningrise respectively, had Mike growling in a more high pitched Black Metal style. He switched to lower growls after these two records (and also when he recorded Brave Murder Day & Sounds of Decay with Katatonia).
With metal overall having evolved so much since the 80's, I dont think anyone these days will accept a growler who isn't talented at what they do. When you learn to appreciate growling, you realise how much of a fine form for vocal brutality it serves, and also that it requires a LOT of skill to master.
I personally now have more respect for a good growler than a good clean vocalist.