Don't cook a brisket to a level of doneness, cook it to internal temp of at least 190, and preferably 195. If you don't cook it to 190 or higher you better have chainsaws to cut it.

There are others on the forum who can give you excellent advise on brisket. As a brisket newbie, I can tell you one thing. Brisket rare or medium rare will be so tough that it will be close to inedible. Brisket is a classic lo-n-slo cook, where the meat is ever so slowly brought to 190+ degrees, thereby melting the tough callagen without drying the meat out.

I think the NakedWhiz write-up is very good. Like everyone else has said, medium rare brisket will be less tender than well-done shoe leather. I cook mine at 230 degrees (+ or-) until the temp begins to climb out of that 195-ish plateau. One time I let it go for a while after it exited the plateau and the meat went from firm and tender to kind of mushy.

Here is the RSM, I have made a few changes however over the past summer. I skip the water, add two tablespoons beef base and for the rub I use Cowtown steak...

Rick’s Sinful Marinade

 12 oz. can of beer
 ½ cup cider vinegar
 ½ cup of water
 ½ cup Worcestershire sauce
 ¼ cup olive oil
 1 tablespoon beef base
 2 tablespoons barbeque sauce
 1 tablespoon Season salt (or your favorite rub)
 1 tablespoon celery seed
 1 teaspoon cayenne pepper
 1 teaspoon MSG

Mix the ingredients and baste as necessary, or add when wrapping at