I played this game for the first time about six days ago, and so far, this game is extremely enjoyable, especially in first person mode, this is extremely immersive, the voice acting is great, the game is actually lighthearted for what it is and most of the content discussed here is played for laughs. This game has been targeted by conservative parents and is a scapegoat for programs like Fox News, but they always exaggerate the content, so I'm going to say exactly what this game has
Violence: Most violent GTA to date, yet not that strong, this game only gets really graphic when you either progress into the story, or get a shotgun, when you get a shotgun, you can see the innards of the person you just shot and in the story, there is some strong gore including brain matter, but some of those deaths are actually played for laughs.
Sex: You can go to a strip club and get a private dance, in these, exposed breasts are shown and you get into a mini game where you have to fondle the dancers and not get caught by the bouncer, if you win, you can either go to your house and have sex with her or get a double dance for twice the money, if you fail, you get kicked out and shot (the getting shot part might be a glitch in my version of the game), there is also some graphic non sexual nudity, including genitals, a parody of anime on the tv in Michael's house which contains tons of innuendo, you can get prostitutes to have sex with you in the car, but you are both fully clothed throughout the entire event, even in first person mode and a sex tape mission in which pubic hair is shown, this is the content that I have encountered so far, there is probably more.
Language: Every swear word imaginable is thrown at least 10 times.
Alcohol and drugs: You can get drunk after taking too much alcohol, you can casually smoke and do drugs, there is a mission where Michael takes a very strong drug and thinks that he is killing aliens with a mini gun, Trevor has a meth lab.
Overall amazing game, highly recommended for ages 16+.