“It is not the strongest of the species that survives, nor the most intelligent that survives. It is the one that is most adaptable to change.”
If I knew that the All Souls trilogy focused more on romance before starting it, maybe I would have a different perspective. With romance, I have to like the main characters and their relationship, but that's where this series failed.
Diana has disappointed me too many times. Matthew gives off a bad aura. Their relationship is borderline toxic. Matthew and Diana are codependent and can barely function without the other. When two lives intertwine, there will naturally be some dependence. However, their relationship is unhealthy and has an exaggerated and dramatic soap opera type of vibe.
By the end, I'd had enough of Matthew and Diana and everything related to them became ridiculous. They both have a superiority complex and expect others to do what they say without question or opposition. It doesn't help that Harkness puts them both on pedestals.
Diana is the queen of Mary Sues. She's an extremely powerful witch and while her abilities are interesting, they are vague and difficult to visualise. Throughout this series and especially in The Book of Life, she keeps on gaining unique abilities and can do any type of magic. It feels deus ex machina. Also, guess what Diana's sacrifice to the goddess is? It's her sense of fear.