Edgar Allan Poe was interested in many, many topics and wrote about them during his writing career. Though he did write about "death, gloom, despair, and mental illness," as you said, he also had other interests. His gothic or dark stories were about murder as in "The Tell Tale Heart," and revenge as in "The Black Cat and "The Cask of Amontillado." He wrote about the plague in "The Mask of the Red Death," and torture in "The Pit and the Pendulum." Probably Poe's most famous work was a poem, "The Raven," about the loss of his lover and questions about the afterlife. 

Few people know that Edgar Allan Poe wrote what we would call dark comedy. An example of this is "The Angel of the Odd," a story about a drunk. Additionally, he wrote "The Balloon Hoax," which was published as an article in the New York Sun in the mid 1800's. People thought it was true, but it was completely made up by Poe.  

Along with horror and mystery, Poe also wrote adventure stories!  "A Descent into the Maelstrom" was about three fishermen encountering a hurricane.

Then, there was a love story called "Eleonora," possibly based on his great love for Virginia, his wife.

Poe was a man of great talent, whose stories and poems inspired many other writers throughout the years.