Flame of Sevenwaters is a departure from the Sevenwaters series as a whole, more straight up quest fantasy than romantic fantasy. Although Maeve does find love in the end (not a spoiler for anybody who has read any of Marillier's work before), the relationship does not become a romance until nearly the end of the book and is harder to predict. In a way it seems too sudden, but on another level it is an inversion of the classic fantasy scenario in which the hero saves the day and is rewarded with the love of the heroine, whether or not there was any sign of it before. And before our heroine saves the day, at least she and the man whose love serves as the reward had spent some time in each other's presence.
I don't know if Flame of Sevenwaters is the end of the Sevenwaters series. It is the third book about this generation, so it's the natural conclusion of a pair of trilogies. If it is the end, it also ties the entire six book series together as the story of Ciaran, Maeve's great uncle, who was born during Daughter of the Forest to Maeve's great-grandfather and a faerie woman, who reappeared in Son of the Shadows, whose daughter was the heroine of Child of the Prophecy, and who in the end plays a pivotal role in the defeat of Mac Dara.
The end of this book seemed to drag on a bit long, perhaps to give us more time to see Maeve and her fiance as a couple, perhaps to give us more time with the entire family as the series ends. That aside, this is an excellent story about family, fate, and the capacity to do things that you thought were impossible.