The new product's features were so ordinary that consumers were underwhelmed.

underwhelmed 是动词 underwhelm 的过去分词形式。underwhelm 由前缀 under-（表示"不足、低于"）和动词 overwhelm（压倒、使印象深刻）组成，字面意思是"未能达到足够的印象"，即"使失望、未能打动"。 underwhelmed 表示"感到失望的、未被惊艳到的"，与 overwhelmed（感到非常惊喜/震撼）形成对比。