a photo is pretty much art by most people's standards so the "eye of the beholder" is always the most important part. In my opinion...
For me, my current goal with photo's is to represent the performer in a dynamic pose wiht the fire.
In the past, it's been pretty easy to get some great shots of the fire itself, and very hard to get the performer in a recognisable state for Joe public to see the photo and not think it was just made on a computer.
Like the one below, i like the way you can definitely see the dynamic outline and the way the fire has made the legs look like they are wearing boots (just jeans really).
shadowfire This
Burnoff!! one actually looks like there are stars in the background. They were Xmas tress lights hung on the nearby trees. This way they were bright enough to show up on the photo, as well as looking like the shot was done with nothing in the background but dark sky...
Anyway, a 'good' shot is to me, a point of interest that can be readily seen by others, even if they don't actually recognise it for what it is.