To get a better understanding of your smoke and help you out more, how long, what temp and how big was your brisket?
What method did you use, did you allow it to rest. So many little things can change the outcome by so much.
Glad your chicken turned out great, personally I always brine but even doing that have had some birds not turn out so great so it shows you are definitely doing something right.
Let us know a bit more about your brisket smoke from start to finish and I guarantee you will get plenty of tips to help you figure it out.