Complaining about unnecessarily dark subject matter and suggestive scenes/references is valid, but all the POTC movies have those. You can't dislike a movie for having those things in there, but be fine with the other four movies in the series have those same elements to them. It's completely hypocritical.
Blackbeard doesn't hold a candle to Davy Jones or Barbossa, but he's a fine one and done villain. He certainly has more development than Salazar. They literally explained his backstory in a trailer. There probably should've been more to it than that. The dichotomy between being a brutal privateer and straight up murderer is never really explored like it could have. You get the one scene during the flashback and that's it. With Blackbeard, you feel a sense of desperation in his quest because of the supposed fortune telling of his own doom. He has a drive, and they explore the idea of him as a compassionate father vs. blood thirsty pirate more than Salazar potential struggle.
DMTNT (man I wish they'd gone with a different title, and not the dumb Revenge title used oversees...) also messes up a bunch of lore established in previous films. While At World's End makes the true length of Will's stay on the Dutchman confusing, where did this supposed new crew come from? Will very clearly let everyone go that wanted to go at the end of the film. Only his father chose to stay. So why at the beginning of the film does he try and get Henry off the ship before the crew sees him? Why does it matter if the supposed crew sees him? Will is the captain, they have to do what he says. Why did the Dutchman even come up at that point, and how did Henry even figure out how to track it down? It had to have been somewhere nearby so he could row out to it without getting smashed by the sea and be back in time before Elizabeth flipped out. And when Henry "lifts the curse", who is in charge of ferrying the dead to the afterlife now? It seems like they're just left to drift like we saw in At World's End. By lifting that curse, Henry has ruined the afterlife for everyone who dies at sea for eternity! The writing team didn't put in enough thought to how lifting Will's curse would mess up continuity.
A lot of the film is like this. The characterization of certain returning characters is way off too. Gibbs being ok with abandoning Jack because they're out of cash? Nope. Never. Marty, sure. Scrum, sure. The other random guys? Sure. Gibbs? Never. They might decide to go their separate ways for awhile, but he would never outright abandon Jack. Even in Movie 1, he "kept to the code" but came back anyway with the others to save Jack at Port Royal.
If we had seen their relationship deteriorate over the course of the five films, then I'd buy it, but there is no way the same man who toasted to the voyage to Isla da Muerta in COTBP with Jack would ever leave him and only come back when there was the promise of more money.
Also, where'd Cotton's parrot go? We saw it with Jack the Monkey in the bottle in On Stranger Tides, and then was nowhere to be seen afterword.
It's a bunch of little things like this that bring the movie down. It might have brought Will and Elizabeth back, but their story was wrapped up in 3. We didn't need a continuation of their story. They're arguably the worst things about 2 & 3 anyway since it's because of Elizabeth that the infernal love triangle... well I guess Norrington counts as one vying for her affections as well, so... love square or pyramid or whatever is a thing in those two. That on top of poor characterization and inconsistencies in the canon really hurts the movie. Not really a surprise either, since it was the first Pirates movie not written by one of the original two writers.
Say what you will about Movie 4, but it was a more back to basics straight forward adventure like Curse of the Black Pearl that understood it's characters, while Movie 5 took some of the worst aspects of previous films such as confusing storytelling and churned out a jumbled, if not enjoyable, mess.
Also in terms of the mermaids, all the actresses wore skin-tight body suits from head to neck. There was never actual any nudity in the entire film, or while shooting.