I do think it would be interesting to see how the book would work if the story were framed differently. At the moment, the focus (from the very first line, even), seems to be on the search for the mysterious ‘boy’—so the reader is led to expect a fairly straightforward ‘quest’ plot. Perhaps it is the subversion of this that is frustrating and led to me initially thinking that the first half was largely tangential. If the story were framed so that it was clear from the start that it’s more character-focused and centred on the changing relationship between Tracker and the Leopard (which I think is fair to say is the core of the novel, especially taking into account the title!), perhaps that would help to alter reader expectations a little.