I absolutely loved Blood Bound. It had everything I could want in a good book - a great plot, a kick-ass heroine, a believable love triangle, and wolves.
But what makes the Mercy series so amazing is Mercy herself. Unlike a lot of protagonists - both male and female - she shows a fair amount of common sense. She doesn't run in looking for trouble, errs on the side of caution, and refuses to sit around whining about her problems. Not to mention she has a work ethic I would pay good money for. Just because she was almost killed the night before is no excuse for not turning up to work the next day! Seriously. Mercy is one of the few characters whose judgement I trust implicitly.
Blood Bound focusses on the vampires in Briggs' world - meaning Mystery-Machine-driving!vampire Stefan played a much bigger role than he had in Moon Called. Vampires are never good news in Briggs' world, and Mercy finds herself thrown into the middle of yet another muddle she desperately wants to avoid. We learn so much about the verse in this book - and Mercy learns an awful lot about herself.
On the romance front, the triangle gets a bit of play while still remaining only a sub-plot. What I was most impressed at was Briggs' ability to actually make me like Samuel. Even though I had long ago made my mind up that Adam was the one for Mercy, Briggs manages to make me understand Mercy's hesitation in choosing. For me, this is pretty much a miracle (usually authors who mess with my OTP usually make me want to throw things.) The action in this book would have gotten it a 4.5 stars - but the romantic tension brought it up to the bloody spectacular level!
Bottom line? There is a reason this series is so damn popular. You need to start reading it... now.