I cooked brisket once and it came out awesome. I took this right out of a book from Myron Mixon. He pretty much said yes in traditional BBQ you cook slow and low, but he said that he can cook it just as good at 350, with a water pan and injecting it.
In a nut shell it was like this:
Inject the meat, and stick it in the fridge over night.
Fire up the kettle at 350, fill up a pan with water.
Put your rub on the meat, place in a aluminum pan and smoke it for 2 1/2 hours.
Then cover it with foil for 1 1/2 hours or until the point end temp reaches 205.
Let it sit in the pan wrapped for 3-4 hours.
This was for 15-20 lb brisket.
I sliced that thing and it was like butter, moist, nice ring, and burnt ends on it. I would do it the same way again.
You did 225, 4 hours, and i did 350 about 4 hours....as the other said, didn't cook it long enough i would think.
I know meat temp rises, but in this recipe it was pull the meat out at 205. Marinating it over night like it did i would think helped it out. You just mentioned that you were mopping it.