This book was written in the late 1950's. Messiah had decided to write a book about quantum mechanics for the French physics students. At the time he was in the US. The results of the book was that he learned quantum mechanics in English, he wrote what it knew in French, and it was translated back to English.
The book spends too much time explaining the obvious and then just drops in information without much discussion. He also uses, what is then and today, non-standard notation. (And the use of Roman numeral is annoying.). Many times it felt that he was writing to explain it to himself, in his manner and not to explain it to his French students.
This appears to be a work that is best left to the historical physicists. I am planning to read the second volume. To see if my opinion changes any.
Ich weiß nicht, wie ich es als ein einzelnes Lehrbuch zu Quantenmechanik gefunden hätte, neben den Büchern von Cohen-Tannoudji aber, und ergänzt mit Feynmans und Susskinds Vorlesungen, die man im Netz findet, fand ich es als eine gute Ergänzung.