Being brand new to the site, much of the value I see in this format comes from the ability for back-and-forth, voicing of differing opions, and sharing resources. Citations to sources, resources and tools are always welcome, don't get me wrong. But fuzzier sources of knowing, like experience and expertise are often difficult to share in a more formal setting; the same goes for opinions. I like the ability of the Q&A/comment format to dig deeper and to spark conversations around issues we're all facing.
So to me, what makes a good answer is something that is on-topic, that attempts to bring something new to the thread (that hasn't been covered yet), that is transparent in the source of that content (opinion, outside source, personal experience, etc -- which are all acceptable.), and that is respectful of the asker and the other answerers (even when it offers criticism or dissent).
Of course, this is all just my opinion.