There is a real change in the role portrayed by Bud Abbott in this picture. In past films, he has had the role of Costello's straight man for dialogue scenes. He played a sharp, smart, heavy. No one was meant to take this seriously, but Abbott played the bad guy! He usually gets the best of Costello. (This is not true of their famous "Dice Routine", "The Lemon Bit" and that oh so satisfying conclusion of "Africa Screams".) When it came to physical comedy, Costello was on his own, with Abbott nowhere to be found. But starting with this film, and continuing with "A & C Meet the Mummy" and "Dance with Me, Henry", Bud Abbott has become a buffoon. He takes more pratfalls in this film and in "The Mummy" than he did in all of his other films combined. Now it is obvious that a stunt man is doing the physical bits for him, but it is nice to see Abbott become funny. Why didn't this happen sooner? Maybe it was Lou Costello's ego. Maybe it was Bud Abbott's illness. Maybe Abbott just didn't care and let Costello carry the team.
With "Keystone Kops", the writers have finally made Bud Abbott funny. He tries to be gruff and mean, but it just isn't in him. He tries to show that he is braver and smarter than Costello, but no one believes him. There is finally some depth to the team. Costello is still silly and innocent, but now Abbott is a phony to the world. In the past he was able to fool everyone but Lou.
Now I am not saying that I do not enjoy the previous A&C efforts. Some of them are brilliant comedies and John Grant's routines are always marvelous. However, it took so much time for the characters of Bud and Lou to grow. I only wish there were more films to see their metamorphosis.