I should say I thoroughly enjoy this series, but I'd hesitate to call them 'great' books. They are very entertaining. I won't do a review of all 6 just now because I've been reading them on something like 6 month intervals (the books themselves don't take too long to read). Obviously if you've read the previous 4 books you know this is a loose re-telling of WWII. I won't get into the details of the background and where they significantly differ from actual history (that might appear in an 'Into Darkness' review). As with the previous 4 books, this story is loosely based on one year: 1944. Obviously some important events happened that year, especially the invasion of Normandy and the Warsaw Uprising. Stop here if you don't want to see plot spoilers. Some of the critiques I have for this book are:There is an annoying change of name from 'Boulevard of the Equestrians' to 'Avenue of Horseman' which Turtledove inexplicably (and I'm assuming accidentally) makes for Priekle (Paris's) largest street (i.e. the Champs-Elysees).D-Day takes place in Spain, rather than France, since in this story Spain is occupied by Germany rather than merely being official neutral. A general annoyance is that there is no Siege of Leningrad, no invasion of Italy, no serious Battle of Britain, and basically no coverage of the Pacific Theater. I also find it annoying that Germany is much larger than the US and the Americans and English speak different (in fact, completely unrelated) languages.