I haven't enjoyed a sci-fi novel so much since Neal Stephenson's Diamond Age -- not that Time Past is a derivative of anyone else's work. This is a new style of writing space science fiction that I haven't seen before.
The characters in Time Past speak and act like real people: they don't have the theatrical quality and stilted speech of many sci-fi characters, who have to 'explain' what the book reader can't see or hear. You don't get spoon fed each fact just as you need it, the way you do in television scripts. But this also isn't one of those books where you're left guessing at the end.
The best sci-fi novels have always offered a 'point' rather than just being robotized cops-and-robbers. Time Past considers the way we misreport history, making saints and villains out of more mundane folk and ascribing every event of their day to them, whether they were personally involved or not. It also questions how loyalty and authority work in groups and larger communities. And it considers the trade-off between today's needs and the needs of the future.
That's a lot of weight to put on a book that also maintains a taut storyline and a large cast of characters, humanoid and other. It says something for McArthur's ability to keep the flow of the narrative that I didn't find myself checking back every few pages to see who was who and what they'd done.
At the end of the book I found a short bio of Maxine McArthur. She's an Australian who's lived most of her adult life in Japan. Writing is her second career. Maybe it's having lived a rich life that has enabled her to write books that are both complex and intelligent, and explains her ease with intercultural (interspecies?) relationships.