I loved O'Neill's 1976 High Frontier; I still have two of the books. The orbital colonies came first, then came microwave beaming of solar power as an attempt to justify the beautiful tori. I even had a personal connection, an aunt worked for the O'Neill Foundation for years. Once I considered presenting at one of their meetings, but I couldn't make it fit my schedule.
There's not much left of the High Frontier now. The Wikipedia entry is about one paragraph, though the old visions live on in space operas (science fantasy). Charles Stross, a first rate writer and thinker, is old enough to have fallen in and out of love with the High Frontier, and today Stross dismantles it. It's harsh reading for folks who, like me, went to college hoping to join the astronaut program, but it's familiar stuff. It's been clear for some time that biological organisms are not going to travel to the stars.
Inorganics, yes, organics, no.
I think he's a bit pessimistic about the rest of the solar system however. If our civilization manages to survive a few hundred more years the energy and environmental challenges may seem pretty doable. It just won't happen as fast as Kennedy once imagined.