Heres a few questions Ryan......what are you smoking it in? did you have a constant therm temp? do you have pics of the slices? Here's my 2 cents.....so take it for what its worth.
I spray mine down every 60-90 minutes during the smoke. I cook fat side up the whole way, but that is matter of preference, i've seen it done every way possible. The "theory" is that as fat renders it melts thru the meat, but that's also a matter of opinion. 170 might be a little early to foil, unless you are running out of time and need to crutch, otherwise try 175-180. 17 hours for 12lb brisket prior to trimming (so i'm assuming 10lbs?) seems a bit long, but briskets can be a fight, regardless of size. Also, don't forget to mark your brisket for cutting later. Take a corner out of the flat so you know which way the grain runs.
Keep trying....cause when it's good, it's GREAT. Otherwise, I can think of many things you could still do w/ the pieces.