Voted Below Average on this one. First time in a while I've rated any of the novels lower than Average, but this one just never came together for me.
I felt that the two story structure, even though the stories had a certain resonance with one another, really weakened the book overall. They both wound up getting short shrift. The 2380 story would have been problematic anyway, given that we knew the outcome in advance. I'm pretty sure it had already been mentioned somewhere that Jasmine Tey was the one who rescued Rebecca and formed a subsequent bond with her. I also didn't find Radovan a particularly compelling character, so those parts just felt a bit uninteresting to me. I did find the descriptions of Rebecca's viewpoint of the events to be quite good, but there wasn't that much of that.
Similarly, it felt like there just wasn't that much to the 2386 story, either. It took too long to really get going, and parts were too predictable. I had figured out what the Glant were doing with the children long before Sisko did, so it felt like it took forever for him to figure out something that seemed pretty obvious. I was also disappointed that there wasn't more exploration of who or what the Glant were exactly and why they had chosen to isolate themselves from other species. As someone else noted, they seemed awfully unaware of their own natures for beings that depended upon other organisms' own consciousnesses in order to reproduce.
Finally, I thought that Rebecca really was reversing time, not creating new timelines or jumping from one timeline to another. In trying to wrap my head around that, I decided it must be some sort of a localized effect, rather than the entire universe backing up in time and then moving forward again. The only two examples of it we got involved changes that went back only a few minutes, so it seemed like that would work. It probably doesn't hold up scientifically, but at least it gave me enough of an answer that I could keep on reading.
In the end, it felt like too much of the point of the book was the final revelation about Rebecca. Although that is significant, it seemed like a relatively small point to build an entire novel around.
I really wish we could get more authors involved in the main DS9 storylines and go back to the kind of tightly-plotted, intricately-woven books we were getting in the early relaunch. I know it's probably not realistic in today's economic times, but it's still what I'd like to see.