Flannery O'Connor damned the novel with pretty faint praise when it came out: "I think for a child's book it does all right." That seems unduly harsh (and unfair to YA literature). What works best for me as an adult reader is the slow accretion of local color, the barbed social comedy, and the graceful prose.
After my diagnosis, I felt my own fellowship form. My parents came together to do their best to protect me; they protected me from germs, infections, depression, and loneliness. My best friend and sister provided levity in a dark time much like Merry and Pippin. I met another cancer survivor who proved to be a great guide on my journey, showing me the path to recovery.