For example, as I read through Gav Thorpe's Eldar books I'm kind of clutching to my old interpretation of the Eldar, how the Path works, questions of technology, and so on.
I take you mean "The path" series by Gav which is excellent, the Pheonix Lord books are also worth reading. The Ynnari books, although well written and did flesh out Eldar a bit felt rushed towards their end, and I really didn't like that gem of Khaine thing (phrased in a way to avoid spoilers) as it invalidates the point of the young king.
I kinda prefer the older, unknown, horror-inspired Necrons.
Yeah I got to agree, for me the old Necron's made certain amount of sense given their lore, bent on the destruction of all life, now they feel more like a chaotic neutral element.
The lore feels like we are a few books away from Imperium, Tau , Eldar and Necrons holding hands as they slap chaos back into the warp, then route orks into helping them clear the Nids off.