I just finished "The Art of the Impossible", which I found very enjoyable despite the fact that it mainly followed original characters. I really liked how many vital bits of Trek backstory were woven into a single story that touched on the lives of so many important characters. I can't even remember all the events that happened such as the origin of Worf and the death of Troi's father. I also liked seeing the conflict between the Klingons and Cardassians. I liked how comically petty and inept most of the Klingons and Cardassians were.
I don't remember the DS9 Relaunch books anymore but do they establish right off the bat that Dax and Vaughn knew each other and didn't care for one another?
Are the rest of the Lost Era books this important to Trek continuity? I bought the Serpents one by David George so I'll read that now.