adjective

In English there are positive, negative and neutral(both positive and negative) adjectives describing personality traits. My question is that are "serious, silly, talkative,nervous" considered as neutral adjectives? Of course, I know words are used subjectively and it depends on the context or the tone of voice but I'm not sure about these adjectives. To my understanding "silly and nervous" are definitely negative but I've got no idea about "serious". I need the correct answer as the day after tomorrow I have to talk about this topic. Would you please explain it by some examples.
Thank you in advance.