First of all, regarding the book as a book: it is on the familiar -newspaper- paper like all the books in the series from the publisher, which the positive thing is that it makes it light despite its volume, but the negative thing is that it wears out easily.
As for Martin's story: we follow the chronicle of the Targaryen family from its first dynasty to a specific period. For those who have seen the first season of the series, the continuation of the story starts from around page 400 of the book.
Personally, I missed a bit of action, because it's like reading the story through a historical book written by a master about the Targaryens. But still, it is easily readable and keeps your interest in general.

I bought the book after the end of the first season of House of Dragon to read the continuation, the truth is that I expected it to be much better.
The story in the book is in the form of narration, like a historian narrating some historical events.
Many times new names/locations appear without much analysis out of nowhere and you just get lost as you read, while other times there is an analysis of trivial events.
As a book, the paper quality is average, some pages had small creases and the cover was lifting from the first day, overall I consider it to have borderline mediocre quality.
If we also consider the price, which is 30 euros, you are simply paying a lot of money for a mediocre book because the series did well and all this hype has been created