"어때, 좋지?" => How is it [How do you like it / What do you think]? Isn't it nice [good, wonderful]? "How are you, you good?" would be 어떄, 괜찮아? 어때? (어떠해?) is like "How am/are/is I/you/it/they?" with no indication of the subject. 좋지 (좋다) however is seldom used for the condition of people, so we can infer it's about a thing or situation. (There is the expression 사람(이) 좋다 or 성격이 좋다, "He's a nice person", but it's rarely used without the subject) 하루 종일 그걸로 불안해 하더니만.. => (You/They)'ve been nervous about it all day(, and now ...). Here, the subject can't be "I". It must be about the listener or a third person because -더니 evokes an observation. If you say 했더니만 though, it can only be about the first person. For example, 하루 종일 잤더니만 머리가 아프네 (I have a headache after sleeping all day). It's a subtle difference difficult to explain in a sentence, but the 하다/했다 in combination with -더니 gives rise to such different connotations.