Island at War? Loved that one too. The Guernsey Literary and Potato Peel Pie Society was a blazing fast read, and very fun.
First off, its format. It's epistolary, entirely composed of letters written among the dozen or so people who play a part in the plot. Juliet, a young woman, new writer, just survived the war in London, is the protagonist. While looking for a new book idea, she stumbles upon Guernsey and falls in love with the quirky people there.
I won't spoil anything for you, but it is a fun read. The author worked for years to complete it, compelled and urged by friends and family. In the end, she was too ill to finish the final revisions/rewritings, and her niece did this piece of work for her.
Voice is such an important thing. The author did a good job generally of distinguishing among the characters using their writing voice. This is no easy task; most books really only need one voice, the voice of the author or of a single character. I congratulate her on mastering this challenge. Only one other character seemed to have a voice too similar to Juliet's, in my opinion.
Here's another book to add to your to-do list!