Wherein We Elect Our Favourite Novels of… the 1860's, pt.2 (1865-1869)

(Mr Dick in David Copperfield is the other one people usually suggest with, variably, schizophrenia or autism)

Yes, I can see that. But still, he's a minor character. With the Last Chronicle you have a whole Victorian epic, by a writer at the height of his powers, focusing on the intersection of poverty and mental illness, with a central character who suffers from severe clinical depression, who's not always rational, who's tremendously hard on himself and his family, and who you nonetheless sympathize with and root for and respect. I just can't think of anything else like that in Victorian literature.

i've not read any trollope, i will add it to my list (but am i going to have to read the previous 5 to get to the good one?)

No, you can start with it. There are some plot strands that continue from the previous book, which is also very good, so if you care about that sort of thing you could start with The Small House at Allington, but I don't think it's necessary.

The whole series is worth reading, though. I'd say the first three books, though good, are the weakest; after that it just keeps getting better.