The fascinating thing about ASL, and signed language in general, is that modern linguists agree that it shares every major characteristic of spoken language, except for the fact that it is articulated with hand motions instead of speech. The exact same areas of the brain, Broca's Area and Wernicke's Area, affect the production and comprehension of signs as they do spoken language, and deaf people with aphasia will find their abilities to produce or understand hand signs affected in the exact same way as a hearing aphasiac finds their ability to use spoken language affected.
ASL itself is a linguistic creole, a mixture of French Sign Language, or LSF, and several home sign systems, especially Martha's Vineyard Sign Language, or MVSL, a sign language used by the deaf population of Martha's Vineyard, which once numbered into the hundreds. MVSL itself has laregely been lost to linguistic historians, who now study the development of ASL and sign language in general avidly, but some of it can be tentatively reconstructed from the differences between ASL and LSF.
There exists an expanding genre of artistic works produced in ASL, including storytelling, which is considered one of the cornerstones of the deaf community, and even a large body of poetry.