be a revelation

To be different than one anticipated, often in a good way. Dana's performance in the play was a revelation—I had no idea she was such a talented actress. I was skeptical going into it, but the play was a revelation! I enjoyed it immensely! A: "Did you think their new album was a revelation?" B: "No, but it wasn't bad."

come as/be a reveˈlation (to somebody)

be a completely new or surprising experience; be different from what was expected: His performance in the race today was a revelation to everyone. ♢ My trip to Texas was a revelation.