John David Washington shines as Stallworth. He gets across the character's earnest belief in the system, which simultaneously exists with his frustration when confronted by the racists and other bad apples on the force. He's a character who is sometimes fierce and sometimes fearful, but always believable. He plays especially well off of Adam Driver, particularly in scenes where Flip confronts his own heritage as a Jewish man.
BlacKkKlansman is based on the memoir BLACK KLANSMAN by Ron Stallworth and it takes many liberties to make the story more cinematic. After all, a cop story needs shots being fired and an explosion.
I think the best change is that the movie adds women to the story. Laura Harrier plays Patrice, a militant young woman who organizes campus speaking events and marches and believes the police can never be trusted. She's based on actual women who worked with the Black Panthers and other radical groups. She's intense, but can also slow down and discuss which films and stars she likes best. On the opposite side, a woman is added to the Klan group as well, a wife whose efforts to host go unappreciated. It's an excellent portrait of how these women get wrapped up in supporting and championing a cause that sees them as second-class citizens.
By turns, BlacKkKlansman is hilarious, exciting, and a punch to the gut. I was crying by the time I left the theater, due to Spike Lee's effortless connection of the events of the past to the ones of the present. He's a masterful filmmaker and he's made a movie that's both an entertaining summer comedy-thriller and a haunting piece of art. I thoroughly recommend going to see it, or renting it once it is available on video.