I adore well-developed and fleshed out characters in stories. Alex Steward has shown herself to be strong, resourceful, loyal, and maddeningly stubborn throughout this series. Similarly, Ben is back and as lovable and enjoyable as ever.
I'm going to try and avoid spoilers-this is a great book, and you don't want me giving away the story before you read it for yourself. That said, this is a bit of a departure from the original trilogy of books. We've left Hopewell behind and many of the characters from Hopewell either do not appear or are only there as cameos. This is not a bad thing, as it allows new characters to be introduced and developed and also gives us a chance to see Alex and Ben reacting to new and unfamiliar circumstances.
Previous novels in the series have established who Alex is within her own territory; now we get to see Alex when she's forced outside her comfort zone. It's worth remembering that wolves (and, presumably, werewolves, although Alex might disagree) are territorial-take the werewolf out of her territory and you're adding a new stressor that she has to deal with in addition to everything else, and this is covered deftly and compassionately throughout the story.
In addition to the road trip narrative, there's a mystery (Alex initially describes it as a treasure hunt, but, come on...) and Alex uses her forced exile as an opportunity to dig into her own family history-things even her grandmother hadn't told her. We also continue to see Alex and Ben building their relationship and, even when the pressures are great, their commitment to each other is extremely satisfying to witness.
As others have said, this book can easily be read without the background of the initial trilogy. While there are references to previous events, they are sufficiently explained to within the story so that you never feel lost. That said, hopefully you will be inspired to go back and read the first three books if this is your first in the series, if only because they deeply enrich the tapestry the story is telling.