It is definitely informal and conversational. One can almost visualize the unnamed narrator speaking to you, or anyone who might be reading the tale, as he describes the life and death of Emily. The story begins, "When Miss Emily Greierson died, our whole town went to her funeral." If this was a formal language register, it would read something like, "Miss Emily Grierson, born 1898 in ___ County, died of undisclosed causes at her home. Her funeral was attended by many local residents."