I have to agree that the 70's Queen beats the hell out of the 80's stuff. Sometimes they seem like fully different bands.
It kinda seems like after Jazz they decided that they wanted to become the world's biggest rock stars (not a bad thing) but in doing so they seem to have lost a lot of their best aspects. They probably realized that sacrifices had to be made in order to become huge on the pop charts..... Or maybe it was more simple, they fooled around with new technologies (the Game, Hot Space) and it sold really well (THe Game, at least) So they continued
I think their approach, probably most significantly Freddie's, changed at the end of the 70s. I think he'd proved himself musically with the 70s material and wanted to do something different, encompassing the new technologies and becoming more commercial. He even said as much in a 1984 interview for The Works. He said that he took Radio Ga Ga and made it "more saleable". So I guess that was the way he was thinking during the 80s. He did the same with AKOM.
I feel John was more pop oriented, but Roger and Brian were keeping more rock based, but Fred's influence came over strong, and again this, by his own admission, was more on roger and john's stuff as they were more willing to let him get involved than Brian was.
So my opinion is that the 80s stuff was just different. The music was less intricate, simpler, with less complicated arrangements and melodies etc, and that did fit more with the times. The 70s was about bigger and brasher rock music, but the 80s was "simpler" for want of a better word. I think to remain "successful" they needed to go the route they did.
Tatterdemalion and the junketer
There's a thief and a dragonfly trumpeter