The story is fun, action-packed, and the characters are solid enough. The technical chitchat about the “timeline self-intersecting loop” (a.k.a. “time machine”) made my eyes glaze. The author is a physicist; I imagine most readers are not. It was over my head!
I did find some thought provoking ideas in both the concept of time-travel (whether one travels back into their own universe or an alternate) and in the theological debates, though they both got a little repetitious. The tests to the characters' faith(s) nicely ratcheted tension.
I found the descriptions of the setting a little too light to make me feel completely immersed. It was suggested that the characters saw a lot they'd come to expect, but that it was "different." I wanted to see more of how it was different, and more (besides the difficulty of male/female social customs) about how the characters experienced this journey through their senses. It seems like it would be completely jarring.
I'd have liked to give this a higher rating than three stars because the writing was decent, because of the aforementioned thought-provoking, because it was a clean read, and because there was plenty of action. But the antagonist was weak and clumsy, and made a poor foil. Then the ending was an obvious cliff-hanger, and the epilogue was sappy.