Leigha
This installment focused on the love developing between Larkin and Blair. While it did improve upon the love story of the last book, it still suffered from pacing issues. Blair shows up toward the last 10% of Morrigan's Cross, meaning they have not know each other that long. Each book is roughly one month of time. So they have essentially know each other 5 or 6 weeks before they reach an HEA. The best thing about their story is the ability to go directly to the romance without having to sketch out the initial plot, unlike Hoyt and Gleena's story.
If you can look past the timing of it all, Larkin and Blair work as a couple and as friends. Larkin has a playful, fun loving side that Blair obviously needs in her life, while she adds a bit of seriousness to an otherwise playboy. The two were given more time to be fleshed out from the plot and each other. We also get a tiny glimpse of the awesomeness of Cian and Moira, which is obviously the couple of the last book.
We still have no idea of Lilith's motivation, but we do get to know more about her inner circle (Lorna and Davey). Honestly, I think I like this series so much because Roberts plays with so many fantasy elements. Witches, warlocks, and ghosts are staples of her writing; adding vampires, time travel, dragons, and alternate dimensions really livens up the plot.
tl;dr While the love story suffers a bit from pacing, the overall series is shaping up to be a home run.