This is one of those books which some people love and others absolutely hate. For me it deserved five stars but there will be other readers, some of whom enjoyed the first few books in the series, for whom one star would be too many.
"Homeward Bound" is the eighth and probably final book in the series which begins with an alien invasion of earth in the middle of World War II.
The full sequence is
WORLDWAR Quartet, starting in 1942: warring human nations forced to unite against lizardlike Aliens from Tau Ceti 2.
Worldwar: In the Balance
Worldwar: Tilting the Balance
Worldwar: Upsetting the Balance
Worldwar: Striking the Balance
COLONISATION Trilogy, starting about 1962: twenty years after the initial alien attack a second fleet full of colonists arrives, touching off a further round of intrigue and war
Colonisation: Second contact
Colonisation: Down to earth
Colonisation: aftershocks
HOMEWARD BOUND: in 2031 an American spaceship arrives at Tau Ceti to pay the aliens a return visit ...
The first thing to understand about this book if you want to decide whether you would be one of those who love it or one of those who hate it, is that the "Alternative History" element is very small indeed. Most of the action happens in 2031, seventy years after the alien invasion, and very few historical figures are recognisable.
There are a few little touches relating to real people - I caught references to Henry Kissenger ("The Doctor"), James Dean (no car crash, he lived to old age) and Matt Damon. And one of the comic touches in the book is a "lizard" (e.g. Tau Cetan) policeman who is clearly a parody of Lieutenant Columbo. But essentially this is a novel of alien contact, not alternative history.
The biggest difference between this book and the WorldWar quartet is that the book is about diplomacy and is not a war story. Turtledove often writes books which contain a lot of fighting, but not all his books are war stories and this one isn't. If you are one of the readers who liked his "Great War" series but didn't like the "American Empire" followup, or if you liked most of David Weber's Honor Harrington books but didn't like "War of Honor" then do not even think of buying "Homeward Bound".
One other characteristic of Harry Turtledove which doesn't bother everyone but which really annoys some people is that he repeats things. A lot. In fact, a very great deal. This is one of those books which has a lot of repetition, so if you are the sort of reader who feels patronised or annoyed when a writer repeats things, you may want to leave this one alone.
Good things about the book: I thought the characters, both human and alien, were well drawn, interesting and believeable. There was some interesting speculation about the likely human cost of early interstellar travel. The sources of tension between humans and aliens - ecological impacts, cultural differences, rivalry for territory, drug trading, and fear of attack, were well explored.
Bottom line, if you're looking for alternative history, a war story or one with a lot of action, leave it alone. If you want to read an intesting speculation about how two races might interact in the early days of interstellar travel, you may find this a really good book.