Ayn Rand placed extreme importance on the power of man's mind, on the genius of the logical mind and self as the main source of fulfillment, success, progress and comfort that exists in enlightened societies today. In "The Fountainhead," Roark is the posterchild of the "perfect mind," of the fulfilled and independent human being. He is what she felt all people should be: proud, refusing to submit to or care about what others feel about you, refusing to compromise the genius and integrity of your mind for other people's moral code, and focused on sheer, efficient, intelligent productivity.
Roark's genius is met as much genius is--with a bit of hesitancy, looking about to gauge other people's reactions before responding, suspicion, mistrust, and a total lack of understanding or respect for the genius that is before them. All of Roark's structures are the perfect combination of beauty, efficiency, and purpose; however, people are so stuck in what they were "used to", what was "normal" and what society had trained them to regard as acceptable. This "normalcy" is the stream--most people follow it, because that's just the path they've always followed. Anything new or brilliant often threatens people's sense of security or what is known. So, Roark's structures are rejected by most people who don't take the time to understand the genius of it. However, the people who live in his buildings, and experience first-hand the ease and comforts of living there, begin to understand Roark's genius. A few other individuals, "sudden springs" of people, appreciate fully his amazing talent. So, for the most part, people are the underground spring, going along, and refusing to diverge from their accepted path that has been there for ages. But a few people dare to appreciate Roark, and dare to employ him as a result. Those sudden springs come from society, but are rare.
So, society's ultimate reaction to genius is rejection and dismissal; however, those who are educated and in tune, or who experience his genius first-hand, are loyal, stunned, amazed and duly appreciative.
I hope that those thoughts help; good luck!