In answering your question, I'm reminded of the age old statement that "Beauty is in the eyes of the beholder." Before you address the components of a good hub, you first need to ask yourself what you think is success in writing? If you are seeking fame and fortune, i.e., keywords and page views, then there are many helpful tools to help you/point you in the right direction. Accordingly, you can structure your hubs around those parameters.
However, if you have a passion for writing and you put words to print that come from the heart and what you truly feel, then, in that case I believe that ultimately you will produce a good hub. So, if your definition of success is composing a heartfelt, thought provoking and compassionate piece you will undoubtedly succeed by practicing your trade.