Parts of speech are always dicey in Chinese. What is a verb, what is an adjective etc. So, In the sentence 你好！， what part of speech is Hao?
Never think of parts of speech when learning Chinese, since Chinese has such concept no earlier than Tang dynasty, which is very short history comparing with Chinese. In fact Chinese parts of speech also have nothing to do with their functions in sentence. Noun could be predicate, verb could be objective, even prep. could be subjective, which is totally different with western languages.