Amazing setup of plot and protagonist, artful setting of two distinct futuristic time periods- not to mention I love a good time paradox story. I was also impressed by the way Heinlein portrayed intellectual property snafus and got into the practical mind of an engineer. I did feel that the setup to the story was better than its conclusion. By the end of the setup, I had already guessed the necessary conclusion, so much of the tension was already gone as I watched events unfold as predicted. I think it's possible to play around with a time paradox story while better maintaining the tension. The ending for the protagonist was in character, was quietly and humanly touching, but I did find it pretty pedestrian and ultimately uninspiring.