The Fountainhead is the quintessentially American movie, and the most stylized and powerful presentation of a radical individualist ever presented on film. Gary Cooper and Patricia O'Neal capture Rand's silver screen, melodrama aesthetic in a way I'm sure will never be replicated, and it perfectly fits the book. The script was written by Ayn Rand, with lines straight out of her novel, and maintains the important thematic elements while moving the story along briskly. King Vidor's direction is novel, and the score by Max Steiner is memorable. This is one of my favorite movies. The story is tense and dramatic, and the ending is sublime.
I'd like to note that the description provided here (I'm seeing this on Google) is terrible. Roark is not arrogant. He thinks for himself and he has confidence. Anyway, the movie is wonderful. Watch it. Find out why this movie triggers that Pablo guy (another reviewer here) so much - and ignore the bad architecture depicted in the movie, it has nothing to do with Rand's story. Howard Roark is supposed to be a genius, but they did not hire an actual genius to design buildings for this movie. In the book, Roark believes form should follow function, but he does not design barren utilitarian cubes (like Pablo wrongly claims). He designs beautiful buildings with high-minded aesthetic ideals and even hires a sculptor at one point, but his engineering is always superior, and he is always maximizing efficiency of space and materials.