You do NOT understand Duke. Duke as a character isn't "edgy f-bombs, sex jokes and unironic testosterone", he is the insane man in a straight-laced world: Ever since Duke 1, he was designed as an explicit parody of macho action heroes, and indeed, if you were to play 3D, you'd realise that Forever missed the point, not just of who Duke is, but of what Duke as a franchise is meant to be.
In 1, 2, 3D, and the spin-offs, most of the jokes were built around either loving homages and nods to the films that inspired the Duke, such as the 3D level "Pigsty" opening up with Duke saying "I'll be back!" as a car rams into a police station, or absurd nods to the culture of the times, such as a billboard in Manhattan Project advertising a show called "I Married a TR**NY!", spoofing shameless, exploitative reality TV from the 2000s, or the entire bit involving the "society for preparation of the canine hamburger" in 3D. And whenever the jokes DID delve into sexual material, it was usually a lot more tasteful and subtle as opposed to what we get in Forever.
Duke Nukem Forever on the other hand ditches any form of tact, art or taste in favour of being a mean-spirited, spiteful parody of modern gaming where most of the humour comes from people being assholes, Duke being treated as the greatest thing in the world, and obsession with the act of placing the penis in the rectum. The "signature of Duke" is NOT there, and if it is, it's been perverted beyond all recognition.
In fact, saying that Forever is just like the original games is WHY Forever killed the series, why the franchise has attracted a slew of anti-SJW douchebags, and why shitmeister Adi Shankar is now going to finish what Forever started and kill the Duke once and for all: Critics of the time (and even today) say that the game is just like the older entries because they had no interest in said entries, and this resulted in casual gamers wanting nothing to do with Duke Nukem as an IP. So yeah. You are wrong on so many levels.
(And don't even compare this to the Star Wars Prequels; those movies are different from the originals, but they still understood the core of Star Wars and are honestly really good. Unlike Duke Nukem Forever.)