As the ideological enemy of the west over the past century, any sort of accurate or unbiased biography of Lenin is hard to come by. Of course, one written by his wife will be biased in quite the other direction, but I believe that it is still invaluable as it gives a glimpse of the human side of Lenin that so many, even Marxists Leninists, do not really consider.
Krupskaya's book is more of a memoir than a structured biography, much of it feels like a stream of consciousness of the times when she was with Lenin, rather than a narrative that traced his entire life. Sometimes there were details that were unnecessary, that muddled or lengthened the book, about random figures that had nothing to do with Lenin or the Bolshevik Revolution, though I was not sure if this was more of a Russian sort of quirk or Krupskaya paint as detailed of a picture of not only Lenin's life, but the times of Europe and the places they would travel to over the period of his exile.
Interestingly enough, she does talk much about the tension between Lenin and Trotsky, particularly in the earlier years when Trotsky was aligned with the Mensheviks against Lenin in their own power struggle in the early 1900s over the correct line of the communist movement. As this book was written in 1933, years after the controversial Lenin's Testament reveal, it creates a mystery over what the true relationship was between Lenin, Stalin and Trotsky in Lenin's late life, and what inconvenient truths might have been shelved, or possibly even fabricated, in order to preserve the fledgling movement's integrity amidst global antagonisms.