The first book is probably the weakest in the series due to the character development of the cafe staff and the repetition. I blame that on the author’s background as a screenwriter. You could tell he was still getting his feet wet as a novelist.
I also wasn’t thrilled with the way some of the stories wrapped up. They often involved a woman sacrificing her life (whether it was her dreams or her own survival) for someone else. For example, >!a successful businesswoman gave up her restaurant and contritely went home to run her parents’ hotel at the insistence of her dead sister!<. That said, I still liked the book because it made me think about what I’d do if I could visit someone from the past. It also exposed me to a different culture with a different set of values from my own.
So far, I’ve read the second book, and I think it’s much better. The character development is stronger, as we get backstories on Kazu and the cafe ghost. That said, if you’re not enjoying it by now, your feelings probably won’t change. There’s nothing wrong with spending time on something else you do enjoy.
I own the first 3 books, but haven’t gotten around to the third one yet (my tbr is a mile long). The second book has the origin story for the ghost. It’s sad, as you’d expect, but also insightful.