In Japan, tempura batter is intentionally plain. There are two reasons for this. Firstly, the batter is meant to be subtle so that the flavor of each ingredient can come through. Secondly, tempura is typically enjoyed with a dipping sauce or salt, depending on the restaurant. Some places serve it with a sweet sauce, such as on top of a tempura rice bowl. So, it's normal for authentic tempura batter to be plain in taste.