This doesn't hold up -- there are lots of challenging books that were well-received by the public, and Harrison's Light and his Viriconium books were also quite well-received. Their review scores -- at around 4 stars -- are perfectly in line with what you'd expect of challenging work. For my part, I read Light and enjoyed it.

The End of Everything has ratings that place it in the bottom 0.1% of all published books with >100 reviews. This very strongly suggests that an absolute majority of readers found it frustrating or incomprehensible, and that among those readers are some who had enjoyed his other works.