According to ESRB, this game contains: Animated Blood & Gore, Animated Violence, Strong Language
The so-called mature premise of Kingpin revolves around a fallen gangster who is now out for revenge and domination over the underworld. No heroic macho lead character or buxom heroine here, just a thug out to do no good. While politically incorrect, it's certainly conceptually interesting and has a similar appeal to films like GoodFellas and Pulp Fiction, which also revolve around bad people doing bad things.
Make no mistake, this is just another FPS with some great ideas (my personal favorite was being able to assemble my own crew) and stunning visuals that ultimately go to waste. Dale pretty much hits the nail on the head when the refers to Kingpin's creative direction as nothing more than 'dressing' with corrupt intentions of exploitation.