I'd read that book for the first time only about a year ago. It has some warts, but in general has aged spectacularly well.
It is weakest on predictions of the significance of specific technologies, many by those directly involved in their development or promotion. Some of those have panned out (most notably, of course, information technology), but most haven't, proving impractical or nonviable, occasionally socially unacceptable.
The cautions about psychological overload are strongly on-point.
Where the book is likely underappreciated is in its predictions of social change. These have largely been so successful, especially about youth culture, gender, and race, that the prior state seems utterly foreign to anyone born afterwards. The predictions to a large extent are our present reality, and seem trite simply on that basis.
(This is a general challenge in forecasting: unsuccessful forecasts are glaringly obvious, successful general ones are too ubiquitous to be apparent.)
Toffler cites a great deal of research (though in following up on his footnotes, some citations seem inaccurate), and both the original sources and subsequent works citing them are of interest. He leans particularly heavily on Herbert Simon, a polymath (psychology, sociology, economics, mathematics, AI) with many powerful insights (and a few blunders).