Badass Decay: The Lessening Society in general, as of the last two or three books. As the focus has shifted to Xocr and the Band of Bastards as the new threat to the Brotherhood, they've gone from being a well-organized, professional force of supernatural killers to a loose band of psychopaths led by someone only ever referred to as "Little Shit". Oh, they're still a threat, of course, but not nearly what they were at the beginning of the series.
Although, it is stated that the war ebbs and flows like that, and has done throughout history. However, with Butch being reborn as the Dhestroyer and Xcor wiping out every Lesser in England and perhaps beyond, the Omega is certainly on the run by this point.
Crowning Moment of Sadness: Wellsie, her unborn son, and her cousin, Sarelle, are slaughtered by the lesser Mr. O in Lover Awakened.
Jane being murdered in Lover Unleashed and Vishous's desperate flight to save her was this Up to Eleven for some readers.
When it seemed like Xhex was going to die as Lash's prisoner after the Brotherhood had found where she was being held but had no idea she was still there thanks to a barrier which trapped her in a Pocket Dimension as if she was a ghost.
Pretty much par for the course of the BDB series. Each book will contain at least one monumental Tear Jerker.
Butch and Vishous have continuing UST, even after both find mates.
Phury and Rehvenge kiss in Rehvenge's office, though it is played more as a dominance thing than actual attraction.
Recently, Qhuinn and Blay, and Blay and Saxton.
V and Butch have skipped way past mere Ho Yay in Lover Unleashed.
Wrath once kissed Rhage on the forehead, as a token of respect apparently.
The Omega rapes his male recruits as part of their induction into the Lessening Society. At least one of said recruits is implied to enjoy this.
There's a missing segment cut out of the first book because Ward's publisher's felt it was too controversial to include. It consisted of the then-Forelesser Mr. X going to his young recruit Billy——who had been explicitly stated to have just turned 18 like a week ago——and proceeding to reach into his pants and stroke him to orgasm.
Mary Sue: The author may have hung a pretty clever lampshade on it in Dark Lover, as Wrath is getting Beth's name carved into his back:
She nodded, wondering why she couldn't have been named Mary. Or Sue. But no, she had to be nine-letter Elizabeth.
Why Don't You Just Shoot Him?: Seriously, why do the Lessers even bother trying to throw down with blades or clubs or hand-to-hand with the Brotherhood? Centuries-old warriors that have mastered most forms of combat, and the pale boys go in for fisticuffs. So why not invest in some cheap Glocks and just shoot them?
That is indirectly explained in the books. It's mainly because they don't want to draw attention to themselves and shoot-outs in alleys and abandoned buildings are not a good way of keeping a low profile. If the Lessers can do it without drawing attention from cops or other humans then they'll do it, but keeping the war secret is more important than the advantage using guns all the time would give them.