The game has a lot of Adult content and themes.
Just off the top of my head there is Blood, violence, murder, slaughter, slavery, racism, torture, sex (Not just with companions but there is a 'romance' between an unlikely pairing you can interrupt), drugs, the using of souls as currency, cannibalism (if you count vampirism as such), mutilation, and sex scenes with companions, and in general content that many parents would not consider suitable for their children. When you move away from some of the larianisms, a lot of this game is dark and very adult in nature. It has its... silly moments, but overall it is mature with a lot of its themes. And you could easily analyze some of them like going into the fear of the loss of self inherent with the parasite, who is also in an adult way trying to seduce you.