40kLore

I haven't read much lore surrounding the fall of the Eldar.

I'm interested in stories that fill in the in-between area of advanced immortal empire and what's basically a Slanneshi cult, similar to how the Horus Heresy books detail people falling to Chaos.

Having not read anything on it aside from the codexs and one rulebook section I can say that the fall just feels like a plot point without context, kind of like "suddenly everyone got bored and decided to become an insane hedonist cult".

Are any of the few books on the subject worth the read as far as filling in that part of the setting? I understand that Phoenix Rising has a prologue about it and there is a flashback sequence of sorts about it in Fulgrim, are those worth the read if I'm currently just trying to find books about the dead spaces in my understanding of the lore?