Geoff Emerick has the privilege of being the man who can claim to have done more direct engineering for the Beatles and subsequently the solo artists than anybody else. He also can boast some serious chops as a gifted engineer in his own right.
In the book, he talks about his experiences, primarily in the control room during sessions, in and around the Beatles. Imagine that your job involved something historic happening over there, in the conference room, and now you're able to tell stories about how the people looked, acted, reacted and changed over time -- that's the intimacy you get with the book.
Interestingly, Emerick thinks like an engineer, and as a result most of his book is recalled by way of engineering milestones (he'll say things like "The next night, we began mixing the track. There was a fair bit of discussion about trying to cut it down to make it a bit shorter, but Harrison was adamantly opposed and we never actually attempted editing it.").
The history starts in the early 60's and goes through to the present. He stays true to his own memories, and tends to avoid recollecting events of which he wasn't witness, so it's a pretty clear presentation of one man's experiences and not so much a wandering set of opinions and speculations about other people's feelings and attitudes. For example, in general he will choose to observe that John came in and was snapping at the people around him and not talking to Paul than to say that based upon the way they were acting, John and Paul had obviously had a major fight in the morning and were angry at each other.
He tends to favor Paul over the others a bit, but it seems to be both a result of his general proximity and emotional relationship with Paul as it is about his value of true musical talent in each musician.
My biggest personal take-away was the humanizing of the process of the art - the Beatles would work for hours and hours and hours to get a specific piece of a song right ... which implies that they weren't some sort of master geniuses who made no mistakes and could play anything as soon as they put their hands to it (though, duh, they're still amazingly talented and geniuses all the same); but rather they were gifted artists who came to the table with more abilities than most, but still had to slave away at their craft to reach the heights that they did -- this is heartening to any artist who strives to accomplish something magnificent.
Another take-away I had was that, in many ways, "the Beatles" was more like 6 people - especially when they went into their studio years ... John, Paul, George, Ringo, George Martin, and Geoff Emerick ... with George Martin and Emerick somewhat replaceable, but still key elements of the original sound, not the music of course. Beatles music wasn't just 4 lads, it was artists making raw material and others openly and clearly having input into the creative process and final product much more deeply than I thought (e.g. George Martin arranged much of the backing music and played on a number of tracks, even though he was "just" the producer).
It gets nominally dry at points when Emerick goes about discussing the engineering and artistic process of each song in some of the biggest albums (e.g. Sgt. Peppers and Revolver), but outside of that, it's a pretty satisfying read.
Overall, if you'd like to see the real humanity of people behind the music of the Beatles, including the artists themselves - and you're interested in removing the "shroud of amazing" without destroying the image of the men behind the music, this is a good book to read.