He goes into so much detail about training to become an astronaut, his first spaceflight, training and planning for the Apollo missions, and talks about so many of the details and complexities of spaceflight that I had no idea about before.
For example, in the early space walks, they didn't consider how difficult it is to use simple tools in microgravity and without a surface to sit/stand on. The astronaut got completely exhausted just keeping himself still while turning a wrench, because when you turn the wrench, it pushes you and starts moving and spinning you, and when you try to correct it, you'll most likely overcorrect and then have to correct that, and then correct that overcorrection, etc.
And the level of planning and training for the off-nominal scenarios is crazy. They picked the top 30ish most likely failure scenarios and practiced the responses to them in simulators until they're muscle memory, and have detailed checklists for hundreds of other ones (which they also practice, just not as much). For example, when Neil and Buzz land on the moon, they'd be awake for about 10 hours, so they had to decide whether the plan was for them to open the hatch and walk on the moon right after landing, or get a night of sleep and do it "next morning". The problem with doing it immediately was that, if something went wrong, they'd have to abort and get back to the command module, but then they'd end up being awake for 20 hours while handling an emergency. On the other hand, they realized that they wouldn't be able to get sleep right after landing on the moon anyways.
His writing style is awesome: it's easy to read, explains technical details in a really easy to understand way, and quite funny.
A lot of people are like "we got to the moon in the 1960s, where's the progress we should have had since then?" but I see the 1960s as the bizarre exception rather than the thing that should be used to set the rule. There was no way the space age was going to happen then, in an era where you're almost sitting there counting each bit of RAM you can afford to send into space. The true Space Age is just dawning now, and it's still early in the dawn; we still have to have massive international cooperation to put a single space station up, we can't do something as basic as refuel in orbit, we just barely started having people in space for commercial rather than governmental reasons... it's just the beginning.
The apollo program drove the need for more computational power, more memory, better guidance and navigation and control systems, better materials, experiments to better understand many phenomena, etc. And after the apollo program ended, the contractors that developed those technologies on NASA contracts could just commercialize them. And the data from experiments, on materials, aerodynamics, combustion, and so on, that is publicly available has made engineering so much cheaper and easier.