As a time travel story it was excellent, there was a time machine, multiple uses of that machine, time travel was a key element of the story, and there was even a time loop. The overall story dragged at many points, especially when he fell into the trap of anti-Christian ranting. Then it rushed far too quickly through the climax.
Why is it that smart scifi writers can't imagine a world where Christians are heroes and live respectable lives? At least the anti-Christian stuff was relatively tame and the rest of the book was good enough to overcome it. The narrator was well casted, he sounded about 23 and exactly like a physics graduate student.