We visited the MIA F Lounge last month while waiting for the BA0206.

Its ok, but like most lounges rather dull. When we initially arrived they was only a few cookies and crisps. However later on (can't remember the time) they provided hot soups and sandwiches.
A variety of drinks were available and all self service, including the soda's which were poured from 2lt bottles this meant most were flat

The lounge wasn't that busy, but most people didn't appear to be on our BA flight.

I would stay in the lounge until boarding has been called if visiting MIA again. We left a little early and its under a 5min walk, when we arrived at the gate, boarding hadn't started and it was very crowded.