Charming book, for the most part. As a (beginner) birdwatcher myself, I love the birdwatching theme and how it's intervowen with Harry and Jeremy's journey. 
Would have been much better if that was the sole focus of the story; the other characters really don't contribute enough to merit taking up as much space as they do. Also, the secondary characters' chapters being in different tenses/persons than the protagonists' is just jarring and makes no sense, since all the storylines take place simultaneously.
Definitely worth reading for the Harry and Jeremy chapters, though. They paint a lovely picture of intergenerational friendship and bring a touch of humour and hope to the painful subject of living with memory loss. Sweet and gentle, and not at all cheesy. A light read, but thought-provoking and heartwarming nonetheless.
I could easily see this story as a movie, especially since birdwatching is such a visual hobby.