This novel focuses on the death, funeral, and immediate aftermath of the 'optimist' of the title, as seen through the eyes of his widowed daughter. The optimist has recently, at the age of about 70, remarried - for reasons it's hard for his daughter to understand - someone very unlike his first wife. He dies a bit unexpectedly as he should be recovering from an eye operation. His new wife is deeply unsympathetic to him in his suffering and after his death. His daughter cares greatly; and recollects the earlier death of her mother and her husband in the war (the novel was published in 1972 drawing on a slightly earlier short story.
There's a very large cast of characters here - those in the hospital (Judge, family, neighbour in the next bed plus family), his second wife's large extended family, and the Judge's neighbours and friends in Mount Salus, where he lives. All are well rendered and come and go just as people do in a hospital environment and at a funeral and in the days immediately following. There's also a period in the novel offering the central figure's recollections of her own childhood, of her mother's parents and of her mother, including in a last 5 years of serious ill-health.
In short, this novel has quite a lot to offer - and it won the Pulitzer Prize in the US when it came out. It has the downsides that accompany its strengths, in the same way as Welty's earlier Delta Wedding, which is focussed on a wedding with a very large cast of characters coming and going. 'Yes I've understood that', I think as I reach the end and the optimist's daughter departs her father's house after a final confrontation with the second wife...'and then what? will her life be different? has she come to understand anything differently?' and so on....The fact that, perhaps, nothing becomes much clearer as the novel goes on - simply this is life being lived - is perhaps, though, just part of its realism as a narrative.