The negative reviews that you find here and on Amazon should not be overly heeded. Although Peyser does not write a hagiography of Leonard Bernstein as some of his fans would prefer, neither does she tear him apart unfairly.
I adore Leonard Bernstein. Yet finding out he was an egomaniac who pouted when he wasn't the center of attention does not take away my insane love for his talent, showmanship, and bravery. Peyser does her best to paint Bernstein as a real person with faults and blemishes. She also did her homework and gives an in depth account of his growth as a pianist, conductor, and composer, placing his concerts, compositions, television specials, recordings, and lectures in their historical context.
As far as what critics have made of her "obsession" with Bernstein's homosexuality, I don't believe a reader in 2015 would see it that way. Now that being gay isn't as big a deal, I don't think Peyser's discussion of it would be that big of a deal. I am grateful that she deals with Bernstein's sexuality frankly throughout the book. It is an interesting perspective to see this icon in this light . . .
I read the last few chapters as slowly as possible. I did not want them to end. And even though I knew this book was published while Bernstein was living and therefore wouldn't get to his death, the book brought him so alive to me, I didn't want to face the world without him.