It's a good biography not just about one man but the beginning of neurosurgery and how society at the turn of the century functioned. His life touches William Osler and William Halsted, as well as Walter Dandy, and you see how long it takes to develop new insights with relatively primitive technology at the time for neurophysiology and endocrinology. In particular seeing the lack of standardization cost lives is pretty shocking, as well as the heroic lengths these doctors are forced to go to save lives including Cushing sucking diphtheria out of a young boy's tracheostomy by mouth to prevent asphyxiation. The biography also doesn't shy from less politically correct attitudes at the time like Cushing joking about women getting the right to vote. Overall, it's pretty educational and descriptive of the times.

Edit 1: Okay a lot of this history stuff is pretty boring to the normal person. To someone in the medical field though it's at least interesting in wondering whether or not I would have the bravery to suck someone's diphtheria out of their throat to save their life before the vaccine even exists, knowingly putting my life at risk. It's nice never being put in that position, but I hope I would for any similar situation in the future.

Edit 2: it's described in other books but the other interesting aspect is the perceived rivalry between Walter Dandy and Harvey Cushing and their respective ambitious hunger for glory and being first. Those characteristics are still present today in surgeons but more circumspect and definitely not widely disseminated in released letters.