While I can concede that I've never read the Nightshade series, I can already tell from the prose that this is way, way overwritten, even for a novel of its respective genre. I'm reading between eight different books and this is just one that I picked up at random. I'm not going to say that it's bad (yet), but I'm reading it with a grain of salt.
I do remember this as the novel that kicked up a fair share of controversy since it was an adult spinoff of the (popular?) YA series.