For most Web metrics, it is clear which direction you want the trends to point towards. A higher number of visitors is nearly always a positive indicator, a higher bounce rate nearly always negative.
Average Visit Duration and Pages Per Visit, however, require more interpretation. For a news and education site, an upward trend for these metrics would probably be desirable, as they would suggest a higher level of user engagement.
On an e-commerce or lead generation site, however, these metrics could represent user confusion as much as user engagement – especially if your conversion rates and revenues are declining.
Before placing great emphasis on the high-level metrics that Google Analytics provides, make sure to understand what they really mean for your type of website, and evaluate them in the context of other less ambiguous metrics.