The Aetherology supplement is mostly color for those looking to give their awakened characters some scenery in the metaplanes. The last five pages does have some gameplay mechanics with seven new spirit types, one new spirit power, and two new spirit skills each represented in both SR4 and SR5 rules.
The format of the document is a "posting" by a character Magister that is quoting heavily from a second character (Dr. Gordon) whom is believed to have gone insane. So both the Magister character and others commenting on the post question whether or not anything that is being posted is real, or the delusions of the original madman. While I respect the color that this provides...I came away from my read thinking that this posting was incoherent.
In general, I imagine if you have been having difficulties describing the metaplanes with enough color in your campaign this document may be of some value to you and I would recommend raising my rating by one star for your purpose. But I suspect that for the majority of us, Aetherology will not be of value and you may consider my rating to be generous.