Here is a thread about the best way to cook brisket. I haven't tried it yet, but it's on my to do list.

http://www.food.com/recipe/kellys-be...riginal-475847

I haven't tried a brisket in an oven bag, but I always cook my turkeys in an oven bag, it always comes out very juicy and delicious.

Here is the recipe we use. We think of it as a three day process although it could be speeded up.
Marinate brisket overnight in small bottle BBQ sauce, 12 oz beer, 1 package onion soup mix (rub on top, fat side up), 1-2 tablespoons of liquid smoke, and garlic if you like, salt and pepper to taste, allowing that onion soup is salty.

slow cooker all day on low, or oven 8 hours at 250. We like to then put in frig overnight and scrape off all the hardened fat, and it is easier to slice cold, then reheat in the good gravy left.

Been about 10 years since I made brisket- now I want some and it's 3 am. Darn insomnia! In the bottom of the crock I place 4 - 6 coarsely chopped carrots, then add the brisket fat side up. Slice a medium onion into rings and layer over the meat. Add 2 - 3 stalks of coarsely chopped celery, and about 8 oz of chili sauce. Gently pour a bottle of beer over it all and avoid washing the veggies and sauce off the brisket as much as possible. Slow cook for 6 - 8 hours on low. I like to make this a day ahead, refrigerating the meat separate from the sauce to remove the fat. Slice the meat thinly and reheat in the sauce.

I detest beer- tastes like dirty dishwater to me- but I like beer brisket.