I think that 『容疑者Ｘの献身』 , in the French translation by Sophie Rèfle, might be the first book of crime fiction I read by a Japanese author. I loved it at the time, and I enjoyed re-reading it in Japanese very much even though I already knew the story.
If you are reading this series in Japanese, I recommend to read the first two books before 『容疑者Ｘの献身』 or at least the second one, 『予知夢』. If you do, you will know how detective Kusanagi and his friend Yukawa are used to working together. In 『容疑者Ｘの献身』, their relationship and relation to the case change a little, and this is something you can appreciate more if you have read the previous books of the series.
I remember that when I read the French translation, I was mainly focused on the case and the characters directly involved in it, and I was not paying too much attention to who the detective was. When I read it in Japanese, it was the other way around. I found it more interesting to see how Kusanagi and Yukawa were investigating the case rather than the case itself. Generally speaking, I was more focused on the characters and I found the very end extremely impactful, something I do not recollect from my first reading of the book in translation.
The series’ identity seems to have evolved over time. In the first book, all the mysteries were linked to a scientific phenomenon and this was the reason why detective Kusanagi had to ask for his friend’s advice. In the second volume, rational thinking, deduction and logic had replaced the physics. In 『容疑者Ｘの献身』 again, we talk more about deduction and logic, but science apparently comes back in 『真夏の方程式』, the sixth book of the series.
『容疑者Ｘの献身』 is a book that I heartily recommend if you haven’t read it yet. It is not my absolute favourite by Higashino so far (we’ll have to look at the Kaga series for that), but definitely one of the best books of crime fiction that I have read in my life.