I heard BRI first after a friend suggested the band, and then I heard Blackwater Park and fell in love with Bleak, and the whole album, then the whole of Morningrise. But I was into that kind of music before anyway! But I did like the mellow side too.
I downloaded BRI to see what the band were like without any knowledge of the band and thought it must be an album made into 1 MP3 or something! But that and Bleak will always be my favourite Opeth songs I think, so they are the first I show to anyone who I want to listen to them, even if those aren't the best choices!