I saw this last night and it was just ok.
The problem with it is that it is a bit tired. If you look at the plot, the jokes, and even the actors themselves, they all look a bit tired.
What I loves so much about the second movie is the nihilism of the comedy. I suspect that this is the Michael Bay touch. A good comparison scene between 2 and 3 are the scenes in 2 where they are in the TV store having the conversation about the bullet in the ass, flaccidity, and his momma's titty; and in the third where they are in the nightclub and Marcus is talking about his sexual problems over the mic, and he does not think anyone can hear him.
In the second film, the elements of that joke were building right from the start of the film; and when the time came to bring those elements together, powerful lulz were had. In 3, the element of the joke had been brought up once before, and it was basically unconnected with the plot. The joke fell flat.
The stuff about God was strange. In 2, everyone is doing the woosha stuff without really believing it. But in 3, they go straight to God. This is a strange plot. Marcus is trying to get out of his vow to God, and finally rationalizing that God knew he was bullshitting. There is a very strange passive aggressive relationship to religion in here, which I suspect is because I suspect the directors, Adil and Bilall, are Muslim. What is Marcus' religion? The ambiguity is intentional. It can be what you think it probably is, but it can also be what can be what the directors probably what to exchange for it. Anyhow, I think this is the source of the lack of nihilism, and presumably, the lack of laughs. But they had to go there, I think, because of the way that Mike gets shot at the beginning. Woosha is not convincing, plot wise.
Which brings us to the strangest point of all. The plot. The plot is, frankly, a bizarre mishmash of jungianism.
Imagine the writers room. The films in the series have not developed a plot in any sense, just characters. One of the writers studied screenwriting under a prof who thought that the Joseph Campbell way was THE way to go, and so that is how Bad Boys 3 goes.
They begin by noting that Mike is a sort of playboy with no origin story. What if they made it so that he felt sort of empty because of a lost love? You mean Marcus' sister? No, let us forget about her. Here is a new girl from High School Musical. And so, in true Jungian fashion, they make it so that Mike got his charisma from a witch. A witch! Jungian literalism. And then he had a son with her that he never knew about, but who is going around killing people. So the son is Mike's dark double.
Mike decides to encounter his dark double, and defeats him, but decides to spare him when he sees himself strangling him in a broken mirror (you cannot make this stuff up). Mike then refuses to fight his son, who then has to decided whether to cast his father into hell. But he decides not to when his mother tells him the truth. His mother then accidentally shoots him in the heart, and then the son is converted to good. The witch is then killed by Mike's true love. Mike doesn't end up with his true love, because that is not what happens in 2019 movies.
At the end, the son is given a chance to redeem himself, and everyone seems to have forgotten that this guy killed their boss and friend of many years.
I hope Michael Bay himself writes number 4.