I myself have only recently turned my sound back on just for the conclave fight so i know when the cystals are coming becuase you can't see them till either people run away, someone calls it, or you're dead.
Just because some of you don't want to hear the sound of a boss yelling doesn't mean it shouldn't be put in the game, Go ahead and keep your sound off... But some of us really want this, I would even go and say the majority of people not posting on the forums would love to have this feature or be indifferent to it any way.
You can also keep everything turned down and only have voice over turned on, You know this right?
It's a lot more expensive to have voices. Both in money and time.
I'm sure if the developers could afford it (time wise as well, not just financially) they'd give every boss ability a custom animation and they'd have their own unique voices.
I remember while testing there were questions along those lines for nearly every mechanic. There are quite a lot of little keys to look out for on bosses that indicate they're about to do something. It's a lot harder to see things in Rift though compared to say WoW as the graphics are far more detailed.
As it stands it felt to me like Rift had more voice acting when it was released than most other games I'd played like it.
In the beginning though there were some bosses you could tell were voiced by the same person. A lot has happened since then so I can't quite remember but there were several other bosses that sound really like Hylas. Over all I'd say it's pretty good.
I agree about Akylios' speech about the dwarves to fit really well into the encounter. Another, more recent, line I like is Caduceus little talk before he engages.
How about for the next raid they introduce they have a competition for people to enter to be the voice of the various bosses ?
Could be a good little bit of marketing too