The first two, definitely. The harder stuff on the third and a few songs on the fourth, another yes. Metal has Jazz, Opera, Classical, Blues and any other number of other musical styles mix in and through out so the harmonies and the opera are not a hindrance, IMO. Proto metal is basically just a modern term to describe the harder rockin' and or heavier bands of old that helped to bring about metal through their influence. Queens early stuff definitely qualifies under that definition.
Just about every 40 and older Metal musician I know has at least Queen II in their collection