I'd expected that Carey's faithful reproduction of the Jerilderie letter style of prose would make this quite difficult to plow through (not that I'd read the letter before reading True History, but still...), but in fact it's a really easy read - very entertaining and (hoary old cliche this) difficult to put down. It seems most realistic, and the characters are completely believeable and human - and it's pulled forward by a strong narrative thread (informed for us as readers, of course, by our knowledge of how it's going to end - "such is life"). Having finished it, one is left with the thought that perhaps that really is how it all happened - it's convincing!
It's not that Carey appears unaware of postmodern claims regarding history, literature, narrative and so on - indeed, the textuality of the novel is foregrounded in the way that it takes place within the framing device of it being an account, collected in several parcels (with introductory notes written by some future historian), as well as the interspersal of newspaper clippings and various other figurings of the 'textual' trope. But this foregrounding functions to bolster the 'authenticity' of the central textual narrative (perhaps in the way that early novels were often set up as 'collections of papers which have fallen into the author's hands', etc - Robinson Crusoe, for example) rather than to radically throw into question its validity or legitimacy; the questioning of history and partial irony of the 'True' in the title is more a questioning of received history in its dominant form than of the possibility of History itself. And it works really well.
