Wall’s writing sometimes tries too hard to match the brute force of Metallica’s playing (he describes one performance as sounding “like some mutant one-eyed alien monster . . . smothered in nuclear dust clouds and the blood of puny humans”). His critical take doesn’t always follow the conventional wisdom; he is far more generous with the commonly dismissed “St. Anger” album than with the band’s latest, “Death Magnetic,” which many considered a return to form. His toughest struggle, though, is competing with the 2004 documentary “Metallica: Some Kind of Monster,” which, as he notes, sometimes flirts with Spinal Tap territory but offers a close-up look at tormented Hetfield, control freak Ulrich and laid-back guitarist Kirk Hammett that’s hard for any biographer to top.

Mark Blake, the author of a well-­received Pink Floyd history, hasn’t had the same kind of access to Queen that Wall had to his subjects. Much of “Is This the Real Life?” is based on more recent interviews with May and Taylor, when they attempted a quasi reunion with the Bad Company vocalist Paul Rodgers. Though the two are thoughtful and well spoken, their comments on the band several decades after the fact seem to come through a filter of respectful diplomacy.

The book is strongest when examining the early life of Mercury, born Farrokh Bulsara to a middle-class Zoroastrian family in Zanzibar. Blake has turned up a number of his friends after he was sent to school in India, some of whom were not aware of the singer’s identity transformation until long afterward. One of his contemporaries remembers Bulsara saying, “I am going to be mega! You have no idea how mega I am going to be!” before he had so much as stepped on a stage.

There is one further similarity between these two legendary bands, and that is the extent to which a death defined their legacies. The way the two books handle these tragic moments reveals much about the authors’ differing approaches, and about the bands themselves.

“Enter Night” largely pivots on the 1986 death of Metallica’s defining bass player, Cliff Burton, in a tour bus crash. Burton, Wall argues, was the band’s freethinking musical conscience, and it was his guidance that differentiated Metallica from their thrash-metal peers. His death was followed by “a bold new pragmatism that ensured Metallica would not just survive, but continue to prosper,” Wall writes, inevitably leading to a multiplatinum band that was “bloated by fame and success and full, suddenly, of the kind of hubris that had destroyed the original rock giants.”

For Queen, of course, Freddie Mercury’s death from an AIDS-related illness in November 1991 forever altered their image. As hard as it is to believe now, given the band’s photos and videos, Mercury was always coy about his sexuality to the public and press, carrying on multiple affairs with men while continuing to live off and on with Mary Austin, the woman who many believe was the one true love of his life. Dodging rumors of his sickness for months, he finally announced his condition the night before he died.

Yet “Is This the Real Life?” offers minimal insight into the psychology of this incomparable rock supernova. “Mercury had always been an enigma, even to his bandmates,” Blake concludes. Unsatisfying this comment may be, but it seems to be true. “We didn’t actually know what was wrong for a very long time,” Brian May says of his dying lead singer. “We never talked about it.”