Queen were straining at the boundaries of hard rock and heavy metal on Sheer Heart Attack, but they broke down all the barricades on A Night at the Opera, a self-consciously ridiculous and overblown hard rock masterpiece. Using the multi-layered guitars of its predecessor as a foundation, A Night at the Opera encompasses metal, pop, campy British music hall, and mystical prog rock, eventually bringing it all together on the pseudo-operatic "Bohemian Rhapsody." It's a lot like Queen's own version of Led Zeppelin IV, but where Zep find dark menace in bombast, Queen celebrate their own pomposity. The appeal of A Night at the Opera is in its meticulous productions. It's prog rock with humor as well as dynamics, and Queen never bettered their approach anywhere else.
Stephen Thomas Erlewine, Rovi