Professional music is called the music that is composed with modern academic technique.
And that means?
Music that implies advanced structural and theoretical considerations and a written musical tradition. Unless I'm not understanding your question?
I do not care what theoritical considerations and written musical tradition a composer has. My main goal is to enjoy the game. Music is one of many things that create a good atmoshere that fits to the things happening in the game.
I do not know much about professional composers, but I can tell you my personal taste:
- The music in PoE was not impressive. I finished the game twice, but I do not remember any of it 1 sec after I stop playing.
- Gothic1+2 and Risen1 were some of my favourite games. But I do not remember the music so well because I played them a long time ago.
- There are 2 games where I remember the music after a very long time:
+ beyond good and evil. I was the only sountrack I downloaded on gog and I listen to it often. "Dance with the Domz" is my favourite. But I do not think this type of music fits to D:OS2.
+ Realms of arcadia3: I made a save in the mage tower in the swamp so I can listen to the music whenever I want. I have no idea what they are singing (is it latin?) but it sound fantastic.
Prof. Dr. Dr. Mad S. Tist 
