Gellert Grindelwald Is A Great Villain (Despite Johnny Depp)
To first address the elephant in the room - yes, keeping Johnny Depp around as Gellert Grindelwald was probably a mistake. Colin Farrell delivered an extremely compelling performance as the villainous wizard (in disguise) in Fantastic Beasts and Where to Find Them, and trading him in for Depp at the end of the movie felt like a downgrade - especially given the physical transformation into yet another Johnny Depp character with heavy make-up and silly hair. But The Crimes of Grindelwald works with the Grindelwald that it has, Depp manages to deliver a serviceable (and blessedly restrained) performance, and Grindelwald's characterization is actually one of the strongest elements of the movie.
Lord Voldemort was a more straightforward villain: interested in immortality and power, and amassing a group of followers who wanted to leech some of that power. Voldemort never offered any pretence of being a good guy; in his own words, he believed that, "There is no good and evil, there is only power and those too weak to seek it."
By contrast, Grindelwald is particularly unsettling because he shrouds his bigotry towards muggles in euphemism - discouraging his followers from using openly hateful rhetoric, and claiming that he's only interested in "the greater good." It's far more insidious than Voldemort's brute-force power-seeking, and Grindelwald is arguably a more terrifying villain because of it. One of the most widely-criticized aspects of the movie is the moment when Grindelwald shows his gathered audience a vision of the future, terrifying them with the threat of World War II and the Holocaust, and using that fear to justify the persecution of all muggles. Critics have scorned the movie for invoking a real-life mass tragedy in a movie about wizards and Nifflers, but we've known for a long time that Grindelwald's rise to power happened parallel to the rise of Nazism (canonically, Dumbledore defeats Grindelwald in 1945).
Moreover, this is far from the first time that a fantasy or sci-fi film aimed at younger audiences has invoked the spectre of the Holocaust. Bryan Singer's X-Men opens with Magneto discovering his powers as he desperately tries to reach his family in Auschwitz. The Crimes of Grindelwald had to come up with a plausible explanation for why a man like Grindelwald would attract so many followers, and Grindelwald invoking the remembered trauma of World War I and the threat of World War II (while professing to be the wizarding world's only chance at salvation) is as convincing as it is chilling.
The Crimes of Grindelwald's Ending Is Pure Harry Potter
A wonderful detail of Fantastic Beasts: The Crimes of Grindelwald's ending is Newt's pet Niffler managing to sneak off with the trinket sealing Grindelwald and Dumbledore's blood oath. The Harry Potter books and movies, from the very start, reinforced the idea that the most humble creatures in the world can also be the ones to save it - precisely because they are overlooked by people like Voldemort and Grindelwald, who value power above all things. Dobby, a house-elf, was integral to Harry's escape from the clutches of the Malfoy mansion in Harry Potter and the Deathly Hallows. In the very first book, Gryffindor's worst student, Neville Longbottom, wins the House Cup because of his bravery in standing up to his friends, and in the final book Neville kills Nagini, who is also one of Voldemort's Horcruxes, making it possible for Voldemort himself to be defeated.
Many people have questioned why Newt Scamander, of all people, is the protagonist of a series about Dumbledore's conflict with Grindelwald (rather than Dumbledore himself). After all, Newt is a shy, socially-awkward eccentric who wants nothing more than to travel the world finding interesting animals and caring for his own menagerie. But it's precisely because of Newt's humility that he is the perfect soldier in the fight against Grindelwald. The dark wizard barely even acknowledges Newt in the movie's final battle, and one of his most precious possessions - something that no one could have forcefully taken from him - is stolen away by a Niffler without him even noticing, because Grindelwald would never consider a Niffler as being worthy of attention.
There are perfectly valid criticisms of Fantastic Beasts: The Crimes of Grindelwald, but the boiling pot of outrage that marked the lead-up to release means that a lot of the hate towards it feels overblown. There are still three more movies in which underserved characters like Nagini and Theseus can be given more screen time and deeper characterization, and Fantastic Beasts' long game can be revealed. If there's one lesson to be taken away from The Crimes of Grindelwald, it's that we should wait until those movies come out to judge them, and perhaps even give them the benefit of the doubt when we do.