Dutch ovens are very useful pieces of equipment and although they serve a multitude of purposes, their design was intended for braising. They are best suited for preventing moisture loss during the cooking process and for maintaining level temperatures. As for cooking a brisket, most preparations should call for you to put the lid on after the liquid has come to a simmer and to leave it on, except to turn the brisket periodically, until the brisket is done. As a side note, I don’t generally use a dutch oven to roast anything as it can prevent the heat from consistently circulating around that which you are roasting.