This is an amazing story, plain and simple.
The setup is interesting and entirely plausible. The characters are very believable and the leadup to their interludes is very realistic. Both have realistic reactions and both have regrets about what happens.
There is a great potential for a sequel here, but IIRC, Gary Johns is no longer writing. Pity.
The writing is top-notch. Not a typo or grammar error to be found. The chapter divisions come at logical parts of the story and don't really ruin the immersion at all.
In addition, the stroke material is top notch.