The expression "face as long as fiddle" is often used to describe someone who looks sad or unhappy. If you want to describe such a person using different terms, there are several synonyms you can turn to. Some good options include downcast, glum, gloomy, dejected, melancholic, morose, crestfallen, or disconsolate. Each of these words conveys a sense of sadness or emotional distress that is similar to the expression "face as long as fiddle." By using varied vocabulary, you can add more depth and nuance to your writing, creating a more vivid and descriptive portrait of the person you are describing.