Harry Potter Books vs Movies

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I was reading Harry Potter books, I was late to read them, almost 7 years after final Pottor movie. Potter Movies were good enough, but Books were better (expect something which should had changed) Potter movies missed many important things like Peeves Ghost, Fred/George as Quidditch players, Ex Headmasters like Phineas Nigellus Black, Ludo Bagman and Winky house-elf (Goblet of Fire) etc. Some have very short roles despite to be important, like Kreacher house-elf of Black Family etc. Movies did not mentioned S.P.E.W. started by Hermione, Ron and Hermione Named Prefects in 5th year, Percy's bad behave and even Dumbledore's story. There were many things missing. What you think was the most important that was missed in Movie?