This is the third Connie Willis Oxford Time Travel book. One more to go "All Clear". Before buying the eBooks I did a little research. Although Time Trave back to WWII did not interest me I trusted Ms Willis' writing ability to entertain me. I am not disappointed.
My research told me "Blackout" and "All Clear" are one long nove. That is correct. "Blackout" just ended.
Ms. Willis creates characters you care about and always includes one sub-story that is light-hearted.
Some problems others have reported is the apparent random use of the Historian's 'real' names versus their Time-Travel names. I had not problem keeping up. The focus is on just three characters 'dropped' at various times and locations in 1940 and only one of the character's names is totally different between current-time and 1940.
Ms. Willis keeps the stories moving with small chapters that more times than not end in a 'cliff-hanger' like in the old serials.
If you want to dip your feed into Ms. Willis' Oxford Time Travel series I would start with "To Say Nothing About the Dog". A farce in set Victorian England and don't let the fact that you won't know what the Bishop's Bird Stump is slow you down.