I read the book when I was but a youngster and saw the film later. Clearly, Alex DeLarge was a role Malcolm Mcdowell was born to play.
I noted, in the film, some discrepancies with the book, all of which were disappointing. For example, in the scene in which Alex and droogs encounter Billy and his gang (intent, at the time, on some serial in-out with a young and rather weepy/creechy little ptitsa, to use Nadsat, the language of the book), the scene ends, per the film, with violence and the rozzers - but not before Alex manages to (unclear) at least partially castrate Billy who "finds himself hanging open like a peapod". Another key discrepancy, and this was especially disappointing to me, given the comic possibility, was after the gang in-out "singin in the rain" scene. In the book, Dim takes the opportunity to defecate on the carpet after everyone has had their turn(s). We're treated to nonesuch in the film, though Dim's repeated toneless singing of "ready for love" lends some genuine comical horror to the scene.
All in all, it was a real tour-de-force from Burgess. Note the blurb about Ebert and his critical eval of the film.
http://www.nydailynews.com/entertainment/movies/malcolm-mcdowell-clockwork-orange-reality-article-1.2516188Another example of actors and the role they were born to play: Lieve Schreiber as "Ross the Boss" Rhea in "Goon"... Other examples?