Roderick's painting and music seem to express the unbalanced state of his mind. They appear to be outward manifestations of his troubled inward psyche and to express his heightened sensitivity or "unnatural sensations." Roderick plays the guitar, for example, in a "wild," "fantastic" and highly overwrought (with "the highest artificial excitement") way:

 It was, perhaps, the narrow limits to which he thus confined himself upon the guitar which gave birth ... to the fantastic character of his performances. But the fervid facility of his impromptus could not be so accounted for. They must have been, and were, in the notes, as well as in the words of his wild fantasias (for he not unfrequently accompanied himself with rhymed verbal improvisations), the result of that intense mental collectedness and concentration to which I have previously alluded as observable only in particular moments of the highest artificial excitement.

Roderick's paintings are in general "vague" or abstract, and the narrator therefore has a difficult time describing them. They evoke an emotional rather than a rational response: the narrator shudders "thrillingly" while looking at them, using the word shudder twice for emphasis. The narrator continues by saying:

 By the utter simplicity, by the nakedness of his designs, he arrested and overawed attention. If ever mortal painted an idea, that mortal was Roderick Usher. For me at least, in the circumstances then surrounding me, there arose out of the pure abstractions which the hypochondriac contrived to throw upon his canvas, an intensity of intolerable awe, no shadow of which felt I ever yet in the contemplation of the certainly glowing yet too concrete reveries of Fuseli.

In alluding to Fuseli, Poe seems to be referencing a famous painting called "The Nightmare," in which a woman is laid out, unnaturally lit, on a slab in a dark room. Roderick's abstract paintings far outstrip the intensity of Fuseli's "too concrete" images. One of Roderick's paintings, however, is not abstract:

    One of the phantasmagoric conceptions of my friend, partaking not so rigidly of the spirit of abstraction, may be shadowed forth, although feebly, in words. A small picture presented the interior of an immensely long and rectangular vault or tunnel, with low walls, smooth, white, and without interruption or device. Certain accessory points of the design served well to convey the idea that this excavation lay at an exceeding depth below the surface of the earth. No outlet was observed in any portion of its vast extent, and no torch or other artificial source of light was discernible; yet a flood of intense rays rolled throughout, and bathed the whole in a ghastly and inappropriate splendor. 

The painting of the vault seems to supernaturally anticipate events to come, but also calls into question how much these events are enactments of the fantasies of a disturbed mind. In other words, does Roderick bury his sister prematurely (while she is still alive, although she appears dead) because he intensely wants to entomb her? (We will leave aside theories that she is an illusion, a projection of himself.)

In the late 18th century, artists increasingly depicted the 'sublime,' often associated with the word awe and often connected with landscapes: vistas of mountains, for instance, where humans are rendered insignificant against the grandeur of the setting. The 'sublime' was meant to evoke the thrilling grandeur of God. Roderick's paintings, though they evoke "awe," push beyond the sublime (the awe is "intolerable")  and into the Gothic, a nightmare landscape of pure terror that reflects Roderick's fevered psyche. 

Having learned that Roderick Usher suffers from a nervous disorder that heightens his senses, the narrator essays to cheer Usher by engaging with him in the artistic endeavors of reading, painting, and playing music, feeling that these aesthetic activities will soothe his soul's turmoil. As he listens to Roderick play the guitar, for instance, the narrator senses the the man's sensitive, creative energies while at the same time, he perceives the inner, dark turmoils:

His long improvised dirges will ring forever in my ears.  Among other things, I hold painfully in mind a certain singular perversion and amplification of the wild air of the last waltz of Von Weber. 

Roderick's paintings, too, transcend "touch by touch into vaguenesses," causing the narrator to shudder as "there arose out of the pure abstractions...an intensity of intolerable awe" that the narrator has ever felt even when he contemplated the "concrete reveries" of Johann Henrich Fuseli, a Swiss-Anglo painter known for scene of horror and the supernatural as in The Nightmare.

Further, the narrator describes a "phantasmagoric conception" of Usher that closely resembles the foreshadows the details of Madeline's death/rising:  

an immensely long and rectangular vault...dark...yet a flood of intense rays rolled throughout.

Certainly, Roderick Usher's artistic endeavours reveal a disturbing strangeness that points to a tortured sensibility from a mind that is  evidently in disorder.