> The book is more an act of self-indulgence on the author's part
That's precisely what it is. And what makes it valuable too: such works of blatant self-indulgence are not very common in mathematics (at least, while remaining enjoyable to read).
> than a profound intellectual achievement in itself
Sure. I would call the book an artistic achievement in the intellectual realm: it talks about ideas, but is art. To put it another way: everyone knows "mathematics is not a spectator sport" — this is usually said in the sense of "you can't learn mathematics unless you do it yourself", which is true enough, but it's also a loss in the sense that there's no equivalent of sitting back and watching a game, watching someone play with ideas and do mathematics. This book comes close. How good the quality of the game is, and whether you'll learn anything from watching the game, is debatable (probably not much), but the experience itself is unusual, which makes the existence of this book a happy circumstance.
That's precisely what it is. And what makes it valuable too: such works of blatant self-indulgence are not very common in mathematics (at least, while remaining enjoyable to read).
> than a profound intellectual achievement in itself
Sure. I would call the book an artistic achievement in the intellectual realm: it talks about ideas, but is art. To put it another way: everyone knows "mathematics is not a spectator sport" — this is usually said in the sense of "you can't learn mathematics unless you do it yourself", which is true enough, but it's also a loss in the sense that there's no equivalent of sitting back and watching a game, watching someone play with ideas and do mathematics. This book comes close. How good the quality of the game is, and whether you'll learn anything from watching the game, is debatable (probably not much), but the experience itself is unusual, which makes the existence of this book a happy circumstance.