BD is right, fat is flavor, render that fat just right and you got some bbq heaven. Go with whole packers too. Don't forget to season the bottom.
You don't have much of a smoke ring cause kegs don't burn hardly any fuel.. less combustion = less smoke ring. If you have a salty rub and let it set on the brisket for about 6 hours that will help a little. Celery salt helps too. This brisket was cooked on a keg ( I fixed my slices before turn in!)
I recently picked up a used 22 WSM and been using that more lately for briskets.. not really for smoke ring purposes but more for temp control. In my case, my kegs have a tendency to get too hot if I'm not super careful, while most people have the opposite problem.