These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Herzgo Alegni, unlike most of the relatively few rapists in the Forgotten Realms setting, likes preying on kids. At one point, he and his warband raided a village, killing all the men and taking possession of the women. Alegni took a woman hostage to force her 10-year-old daughter, Dahlia, to let him rape her. When he was finished, he had his men hold Dahlia upside down to make her more likely to get pregnant before he broke the mother's neck for fun. This is how we're introduced to the scumbag. He also uses a powerful magical sword to enslave Artemis Entreri (a former villain who had undergone a Heel-Face Turn and just wanted to be left alone) as his personal assassin, and used the sword to stab pain directly into Entreri's soul whenever he was pissed or just plain bored. He also commits murder for the pettiest of reasons, like, say, somebody naming a bridge after somebody else besides him, even though he had nothing to do with the bridge's construction.
Matron Yvonnel Baenre, the de facto ruler of the Drow nation Menzoberranzan, is also the most evil Drow yet seen. Yvonnel Baenre keeps the city in its dark, chaotic state while destroying Drow houses she judges have outlived their usefulness. Her own children live in fear of her, and when dealing with her most hatred rivals, the Oblodras, Baenre annihilates their House, sending every inhabitant, even the slaves, to the Abyss to be tortured eternally. Baenre's ultimate goal is to conquer the dwarven kingdom Mithrill Hall, and for this end, she has enslaved the soul of its first king for two thousand years. She also utilizes her Illithid ally to forcibly and painfully mentally torture and devour the minds of those she wishes to interrogate while allowing her children and house to torture those who catch their eye. when she assaults Mithril Hall, her goal is nothing less than the deaths or enslavement of all in her path.
Vendes Baenre, one of Yvonnel's daughters, is just as fiendish as her mother and more monstrous than almost any other Drow. Known and feared for her sadism and penchant for Cold-Blooded Torture, Vendes delights in getting her hands on any possible victim without regards for their crimes. Vendes ruthlessly tortures Drizzt Do'Urden and reveals her reputation in Menzoberranzan is well deserved. Vendes is also known for torturing luckless male drow and turning them into agonized statues to adorn the paths of the drow academies as a reminder to what happens to those who forget their place.
For some, the Dark Elf Trilogy (i.e., the prequels to the first novels), showing more of dark elf society and giving a real look inside Drizzt's head with the first essays, were Growing the Beard. For others, the loss of the more devil-may-care attitude from the Icewind Dale Trilogy in favor of what they saw as Wangst was early-onset Seasonal Rot.
Legacy of the Drow seemed to be more of a downer than the other books, featuring the first death of a Companion, a lot of tension between the characters and years-long separations, while at the same time putting characters in holding patterns for long stretches (for example, Catti-Brie and Drizzt, the resolution of which wouldn't even occur until the end of the trilogy after the next one). But the characters seemed to behave with more maturity, and the implications of some relationships were explored in-depth.
Paths of Darkness continues the trend of dealing with darker and more mature topics in a more ambiguous fashion, allowing yet more arguments from people who prefer different spots on the Sliding Scale of Idealism vs. Cynicism...