I realized just now that I did not do a very good job of reviewing the book, so I’ll add a few more thoughts here.
As I said in a comment, I think that this novel differs from Coetzee’s “Disgrace” not only in subject matter, but in the way Atwood deals with plot and action. Everything that happens in “The Blind Assassin” has already happened. Iris is writing about the past. In this way, it is an extraordinary work because it redefines the reader’s idea of truth.
Atwood doesn’t use plot to propel the novel. In some novels, there’s conflict after conflict, and yet in this novel, I believe that there are very few actual conflicts, apart from the conflict of the truth. Basically, all the major plot takes place in the first 100 pages of the novel, if not the first 50, or the 1st page itself. The rest of the novel is concerned with showing the reader that the truth cannot be trusted. There are two different stories to everything.
Because of this subtle difference in structure, the novel drags a bit. There is nothing to move it forward, apart from Atwood’s deliberate choice to subtly delineate the differences in the two truths we find. The novel-within-a-novel provides imaginary plot that does help ease the dull progression of the first 300 pages. After you start to realize what’s actually happening, the novel becomes much more interesting. You start to make connections; you start to think.