The ending is it's major flaw. There's a rush of confusing revelations about people we've never met and Blandois, the villainous stage Frenchman, who has skulked menacingly all though the action threatening murder and worse, gets swatted without ever having done anything more nefarious than poison an irritating dog.
Christine Ezzard's rather splendid film version of Little Dorrit (the best Dickens adaption ever?) cut Blandois completely and the story made perfect (perhaps better) sense without him.