I'm a music and drama student, and the thing about concept broadway shows is that they pretty much have no plot, but all the songs tie together with a theme. That's where my confusion with albums came in. Should it be defined the same way? Also, I'm not sure if you can claim that the theme of death and 'losing someone' is a particular theme of one Opeth album. Pretty much every album has that in it somewhere. In saying htat, you'd have to say that they are a concept band, but them just about every metal band would be concept. The line has to be drawn somewhere.