What are the most important Facebook marketing metrics?

The most famous metrics on Facebook are propably Fans and "likes" which measure what we can call your followers.
According to the following article there is some Facebook metrics you might not measure.

I think the most important metric is engagement, and "the more engaging content you publish, the more engaging your Facebook page will be." But as logical as it seems, one problem is that marketers do not know fans engagement with their brand because they don't follow and metric this kind of metrics.

You can consider you have a good average engagement rate above 0.1%, and even better, a great engagement rate between 0.3 or 0.5%.  As the article says "the best way to measure engagement is monitor the number of interactions per post, and ideally divide it by the number of fans, that way you get a number that is comparable across multiple Facebook pages with different fan numbers."

Of course there is one thing missing in this article like they don't deals with the fact you can't measure the satisfaction of followers about their online activty. Because as we know brands have the possiblity to "buy" a ceratin number of fake followers you have to be careful with those metrics. Maybe that a good way to improve followers' sentiment would be the addition of a "dislike" button to better understand there real feelings and engagement about our brand.