I came to this with somewhat low expectations, but actually found it a pretty gripping, if sombre, tale of near-future apocaplyse. The viewpoint character, Johnny / Snowman, reminisces about how his friend Crake destroyed humanity in order to replace us with his own genetically engineered version (Oryx being their love). It’s a fairly basic sfnal plot, and Atwood does it competently and coherently; not as good a book as he own The Handmaid’s Tale (nor as brilliant a treatment of the theme as this), but I found it engaging, if somewhat grim.
The gack is a puzzle, to be sure. The middle column of the snippet continues:
but is cut off at that point. In the text of the Narrative of the Life of Davy Crockett, the second quoted passage continues “… go back until I had done it.” so maybe it was merely a typographical error in the original printing: gack for back or for go back.