Anything revelatory reveals something you've never seen or realized before. A revelatory article in a tabloid paper might give you the scoop about a celebrity's (previously) private life.
A revelatory artwork might show you something in a completely new light, like a giant art installation that incorporates the natural landscape around it, or a piece of music that stirs a deep feeling of nostalgia or sadness when you listen to it. People often describe religious experiences as revelatory, and early uses of revelation were also religious, meaning "disclosure of information from a divine source." The Latin root is revelare, "uncover or lay bare."