Forum adverts like this one are shown to any user who is not logged in. Join us by filling out a tiny 3 field form and you will get your own, free, dakka user account which gives a good range of benefits to you: No adverts like this in the forums anymore. Times and dates in your local timezone. Full tracking of what you have read so you can skip to your first unread post, easily see what has changed since you last logged in, and easily see what is new at a glance. Email notifications for threads you want to watch closely. Being a part of the oldest wargaming community on the net. If you are already a member then feel free to login now.

Core books imo

The Silent War: Chosen of the Sigillite (anthology)
The Unremembered Empire
Praetorian of Dorn: Alpha to omega
The Master of Mankind: War in the webway
Tallarn: War for a dead world
Ruinstorm: Destiny unwritten
The Burden of Loyalty

You'll note I've skipped quite a lot and in the other books there are some great stories, sub plots and arcs. However those 7 above imo drive the main story towards the actual battle for Terra.
The others are either continuation of sub plots (Vulkas arc, Khans arc, Maggys arc or are stand alone-ish novels - such as pharos dying light).