This is perfectly enjoyable, but neither his best nor his worst. As he tended to do later in life, this novel ties back to earlier work of his. Kettle Nelly Baldwin from the short story Gulf reappears as Friday's "Boss", for instance. As for Friday herself, she is an Artificial Person, created by genetic engineering, and the genes involved include those from "Mr. and Mrs. Joe Greene", also from Gulf. She has enhanced abilities, and has been working for Baldwin's organization as a "combat courier". The setting is a Balkanized future North America where the nations we know have been broken apart into smaller splinters. One of the big themes of this book is the prejudice against Artificial People (APs), which Friday faces in various ways. She is attacked, goes on the run, and eventually makes it back to her organization, only to have The Boss die and the organization disband. But she has been given a bequest in his will which is specifically to finance her moving off-planet, which she eventually does.

Heinlein is kind of writer who provokes strong reactions, both for and against, in both readers and other writers. For example, see:

https://www.tangentonline.com/articles-columnsmenu-284/1115-remembering-robert-anson-heinlein

http://www.antipope.org/charlie/blog-static/2018/08/dread-of-heinleinism.html

https://www.tor.com/2010/08/16/a-brief-thought-about-why-heinlein-discussions-frequently-become-acrimonious/