In fact, the response to KDE 4 was quite similar.
The problem with KDE 4.0 was that it was simply nowhere near release quality; huge chunks of it were either massively buggy or simply not implemented, and it took them until 4.3 to get it to a state that I was prepared to use it as my desktop. At that point it worked pretty much identically to KDE 3.x, even though the underlying code had been completely rewritten, and I could just ignore the new stuff I had no use for such as activities without it affecting my desktop experience at all.
Unity, while it's less ugly than GNOME 3 and not quite as awful, still shares many of the same fundamental design flaws. No amount of bug fixing and tweaks can make a desktop usable when the basic ideas behind it are so wrong.