[Nick Zwar]

The difference is that if you have lengthy “making of” of classic movies, you usually have seen the movie already. I found Hearts of Darkness: A Filmmaker’s Apocalypse excellent.
A retrospective or making of or featurette may contain many points of view, many subjective experiences and opinions, and that’s all fine.
Liner notes are more like a short introduction to a work. In any case, I prefer facts over viewpoints in liner notes, and ideally, the notes provide context not readily apparent from the music itself. But if it’s interesting enough, by all means, you can also include personal views and opinions. I do have some classical music liner notes where the performers discuss their particular approach to the work, which of course can be very interesting.
I’m open to various approaches to liner notes, they don’t all have to be the same. But by and large, liner notes should provide context rather than interpretation, facts over opinion, at least, that should be the tendency. They should enable me to get a better understanding/appreciation of the music by providing context and background information that is not evident in the music itself.