First of all, i'd question my objectivity on any book that's related to StarCraft, simply because i consider myself to be a HUGE fan of the series and the story. Bearing that in mind, this is my opinion on the book.
The events in the book takes place after the last mission in StarCraft 2 : Wings of Liberty and before the first mission in StarCraft 2 : Heart of the Swarm.
I would like to start off by saying that quite a few people fault this book for being a "filler" or a "bridge" between two StarCraft games...and it really is that, BUT i don't find that to be a fault at all. Why should it be ? The book provided very interested background information regarding the events that happen between two games, and i LOVE that it does that. Above that, the book provided more background about Raynor's and Kerrigan's relationship, and the words "I love you." were finally said! (I'm all for the Raynor/Kerrigan love story so this was a huge plus for me)
I assume that the majority of people who take the time to read StarCraft literature are fans of the series and play the game, and i'm sure a lot of people were wondering what happened between Wings of Liberty and Heart of the Swarm - well, this explains it. I personally found the story very interesting, action packed, informative but also very emotional. I think that Christie did a very good job writing this, given that it's MEANT to be a book that bridges two games, and made the most of it. Story about love, loss, betrayal (actually a lot of that going on), self-finding, trust (or lack there of) and the list goes on. I mean, when you start caring for a "minor" side character, you know that you're on to something good.
All in all, is it as good as Christie's "Dark Templar Saga" ? No. But not because the writing isn't on pair, but simply due to it's limitations as "Flashpoint" wasn't meant to be anything other than a "filler" (and in my opinion, a pretty good one). Is it worth reading ? I say yes. If you're a fan of the series, i definitely this that you should. I personally enjoyed it, but in full honesty, mostly because it was about Raynor and Kerrigan. I can't stress how much i enjoy their relationship, and learning more about it, what it used to be, where it might lead. Both of these characters have lead a hard and unfair life, and yet they still can't catch a break. Finding out about how their relationship started brings a little solace to my mind, knowing that there's a chance at least (PLEASE BLIZZARD) that they might find happiness and peace in the future.