It is free. There are just two fires on either side of the bleacher area where you can roast marshmellows, etc. There is a sing-along with Chip and Dale and a CM ... then 1 or 2 movies are shown on the screen.
It is nice, especially if you have kids -- however, if your visit to WDW does not allow time for this, I don't think you have missed anything great.
Don't get me wrong, it is nice - however, not quite as exciting as a trip into the parks.