CT was probably the person I would (in a theoretical way) most have liked to get to know, as a friend, for long and detailed discussions - because there was so much that only he could have told. But I do feel as if I knew him; because I have read so many of his words, in so many different situations relating to his Father's work.
I always enjoy and appreciate (and re-read) those parts of the History of Middle Earth which Christopher contributed; starting with Unfinished Tales of 1980 (which I happen to be re-reading currently) and continuing up to The Fall of Gondolin (which was published in 2018, in which he said his goodbye).
(I leave aside the 1977 Silmarillion as somewhat of a failure, in which he had not hit his straps as an editor; and which lacks his authorial voice.)
Christopher brought a remarkable (and unexpected) extra dimension to his Father's work, which is probably unique in the history of literature; since it is exceedingly rare to combine such knowledge, talent and dedication with deep sympathy and an apparently complete absence of ego.
Christopher's vast output of his father's posthumous primary writings, and of commentary and scholarship, seems to be motivated entirely by filial love; and this is what makes his achievement so beautiful.