What are three characteristics of Usher?

The narrator of the story says that Roderick's "reserve had been always excessive and habitual." This means that he has always been likely to check his true feelings and impulses around other people, exercising restraint and self-command. The narrator also says that

his very ancient family had been noted, time out of mind, for a peculiar sensibility of temperament, displaying itself, through long ages, in many works of exalted art, and manifested, of late, in repeated deeds of munificent yet unobtrusive charity, as well as in a passionate devotion to the intricacies, perhaps even more than to the orthodox and easily recognizable beauties of musical science.

Thus, it seems as though Roderick Usher has been quite generous in providing charity to others, and he has been passionately devoted to the arts and music as well. The narrator also discusses the fact that the entirety of the Usher family lays "in the direct line of descent." In other words, the Ushers have long married and had children with their close relatives, and this means that Roderick is also the product of incest and may conduct an incestuous relationship of his own.  
In addition, Roderick tells the narrator about the illness that has so altered his physical appearance since the last time they were together.  He says it is "a constitutional a family evil . . . —a mere nervous affection . . . which would undoubtedly soon pass off." This malady shows itself as a severe acuteness of sense: his senses are working in overdrive, so to speak: faint light is too bright, floral odor is too intense, and so forth. He wants to die rather than continue suffering in this way.