Also agree with pretty much all the thoughts here. Would add...and maybe this goes without saying...that what makes a post "brilliant" probably also depends on the person reading it. Beyond the basics of good communication, the other stuff (relevance, originality, a meaningful call to action, etc.) is harder to pin down. The reader is the wild card. What I find original may be old hat to you and what resonates can be very personal. I get a sense of this regularly on Twitter, when browsing peoples' favorites....plus it's fun!