Well, @ogoowinner, it's like that old saying about pornography: "I shall not today attempt further to define the kinds of material I understand to be embraced within that shorthand description, and perhaps I could never succeed in intelligibly doing so -- but I know it when I see it."
To me, a quality post is one that is informative and clear. Entertaining is nice too. Of course formatting matters but hey, what do I know, I'm the guy trying to make the #nopictures tag happen. Length doesn't really matter (even though I am biased in favour of long posts) but too short posts are, I think, the province of the earliest whales of the platform who know that no matter what they're gonna get big-ass upvotes.
So yeah, that's all I've got.