I know that subtlety isn't really Spike Lee's thing, but even with that knowledge, I was still a little surprised by how didactic BlacKkKlansman managed to be—and how much it damaged the overall tone and flow of the picture.
The title of the movie itself sets the tone. It's not enough to simply call it Black Klansman, highlighting the absurdity of Ron Stallworth (John David Washington), an African-American police officer, infiltrating the KKK by posing as a white racist on the phone and then sending his Jewish partner, Flip Zimmerman (Adam Driver), to meet the group in person. No, Lee has to jam in another k, lower case, in case you … what, don't know that a Klansman is a member of the Ku Klux Klan? Did we really need "KKK" in the title? Does it add anything to our knowledge? Or does it, rather, make the title look cluttered and awkward?
Cluttered and awkward is a fair description of the film as a whole. There's nothing wrong with polemic, and Spike Lee does polemic better than just about anyone else in mainstream filmmaking. And there's nothing wrong with being a bit didactic in service of your polemic; the extended sequence in which Lee intercuts Harry Belafonte (playing Jerome Turner) talking about a lynching whilst the Klan members watch The Birth of a Nation, for instance, spends a good long while (successfully) driving home the point about the ways in which media depictions of race can have real-world consequences. But at a certain point you have to trust that the audience is going to understand the points you're making, and that point is probably "having members of the KKK repeatedly shouting slogans from the Trump campaign like ‘America First' and ‘Make America Great Again.'" You don't really need to go beyond that.
All of which is to say that a prologue featuring Alec Baldwin playing a white supremacist in what appears to be a KKK-sponsored film strip discussing the evils of desegregation and a postscript in which we see Donald Trump talking about the aftermath of a white supremacist rally in Charlottesville are repetitive, unnecessary, and distract from the (genuinely fascinating!) story being told. Lee is at his best when he picks a cinematic strategy and sticks to it. I'm a sucker for Lee's manic-didactic mode, a hyper-stylized method of moviemaking that transcends realism to make a broader point (Bamboozled, Chi-Raq, Do the Right Thing), but his more straightforward-storyteller mode (Inside Man, 25th Hour) can be extremely effective as well. Granted, the two sometimes bleed into each other, but the mixture doesn't work in BlacKkKlansman, the power of which is undercut by annoying those who don't need their hands held all the way up to Spike Lee's Big Point.
One last note: The performances are all fantastic, from Washington's Stallworth on down to Topher Grace's David Duke. But Adam Driver steals the show as Flip. He manages an undercurrent of something that might be described as "jovial menace" when he's onscreen with the KKK members he is trying to take down, and Flip's journey from unobservant Jew to someone who understands the danger his targets represent is the most compelling character arc in the film. BlacKkKlansman demonstrates yet again that Driver is our most interesting young actor.