We should take this to another thread. However, if pressed to asked for key moments for characters and the Dark Age as whole, i'd say; Ghost Wars, A Call to Arms, Scorpion Jar, Flight of the Falcon, Blood of the Isle, Swords of Sedition, Fortress Republic Wolf Hunters, Masters of War, A Rending of Falcons, Fire At Will, Last Charge, Ride the Chimera. Bonfire of Worlds as well.
There very readable books i didn't list but their not defining turning points. I didn't list the Proving Ground trilogy only because of readability... however, they were an important part.