The phrase "face as long as a fiddle" is often used to describe someone who looks sad or unhappy. However, there are many synonyms that can be used instead of this phrase to convey the same emotion. For example, you could use the expressions "down in the dumps," "feeling blue," or "morose." Additionally, words like "sorrowful," "gloomy," and "melancholy" can also be used to describe someone who appears unhappy. These synonyms can be useful if you want to vary your writing or speech, as they prevent repetition and can add more depth and nuance to your language.