Depends on the episode. The most explicit episode was "Harsh Mistress." There is sex in other episodes too.
Violence & Gore
Moderate
Varies by episode. Some episodes aren't super violent and are wholesome (like "Memphis", which was violent only within the context of the history). Some episodes such as the guitar episode and "The Execution of Grady Finch" are either graphic or at least violent enough. Depends on the episode.
Profanity
Mild
Never usually downright hard language, but some episodes are more profane then others. Maybe an F-word in one or two episodes. Not really a show for kids. But it's not super hard R graphic when it get R-rated, at least in language.
Frightening & Intense Scenes
Moderate
Depends by episode. Some are moderately intense (such as "Memphis"). Others are downright chilling (the guitar episode and "The Executions of Grady Finch")