If you read our review of the first volume, you can probably guess at how eagerly I've been anticipating this second installment. I won't go too much into the overarching plot in this review, so if you want to know about the vampires and how the main couple met, go check that first review out.
As for Fortunate Beasts, it's definitely a middle volume. These do not standalone. At all. You'll be confused and annoyed if you try. Much remains the same as the first book as for style and setting, with the Night Court and its denizens being depicted in shades of gray, both literally and figuratively. The art is simple but evocative, with Heikkila's exceptional skill at capturing emotion with facial expression and body movement.
The story, however, is different in tone from the first. It's less a story of two people coming together and more a story about two people being torn apart. Our heroes are being forcibly separated for much of the volume, and then there are other (spoilery) issues to contend with. The end of the book isn't as happy as the first, and I would suggest that you don't go into this one expecting the happy sexytimes that we got before.
This isn't to say that Fortunate Beasts isn't still a wonderful book. It is. It's just much different than the first. We still have the same two lovely men and their love is equally lovely. We still have the same scheming Night Court and one heck of a brawl at one point. But things unfold in ways you might not expect. And that's okay. We're only halfway through the story, after all.
In conclusion, I'll leave you with a page that I feel perfectly sums up the book.