I just started playing BD again, and I must say most of the voice acting is pretty horrible. Not the Death Knight though, he's ok.
Also, I'm very confident there isn't a single female voice actor in BD.
Anyway, I think the main reason the voices sound so bad is because they use alot of special effects. I know the intent was good, but the effects on the voices (especially imps) make the whole thing sound strange. There's a limit to how much you can digitally modify a persons voice before it starts to sound unnatural.
Tovi 
