Now I actually haven't read any TL-191 books in person, so I'm curious: Is anything after How Few Remain itself even worth it?
The American Empire interregnum dragged at times, and the characters felt a bit more wooden/cutout-like, but it was still interesting in showing how Turtledove wrote AH without needing war or some other conflict as background on every page.
The Settling Accounts section is where the subtle and obvious repetition (in character attitudes as well as dialogue and scenes) was much more obvious, and the characters felt less distinguishable and more cookie-cutter, yet it still had its decent points, and the action scenes (in the last book most of all) kept me reading.
As a history nut (real and AH), I enjoyed all the books on those two bases alone, to varying degrees. My only advice would be taking a little while off between each book, so as not to be overloaded and make them all seem the same several books in (esp. in Settling Accounts).