I will scroll past all the responses as most do not have the experience I do with this style.
I will work backwards--- and assuming you are not just -- well, a nut case, and something is wrong with your taste buds... I assume something went wrong. I will go with the most common culprit first...
foil - do not foil... period, end of story, neither should you use butcher paper, pans, plastic or anything at all to separate the smoke and heat from the meat.
Next is -- perhaps you are naturally a "underdoer." Now this is not as common as what I write below BUT I will include it here because its affect is nearly the same.
Pepper Usage - Pepper can be used in ridiculously liberal amounts if the process is done correctly. You must also have large amounts of salt... the pepper when placed on brisket has to do two things.... seep into the meat, and only salt will carry it in, and also, BE EXPOSED TO THE HEAT AND SMOKE DIRECTLY FOR A CONSIDERABLE AMOUNT OF TIME IN ORDER TO MILD OUT.
Anyone that has seen my brisket video knows how much I use. The brisket is literally DUMPED into a bucket then slapped on the smoker. But as it cooks, and with NO spritzing or mopping to knock it off it tastes fine. Why? The heat and smoke milds it alllllllllll out. Throw it in foil or a pan or the oven and cover it and you retain all that pepper in the juice and it stays hot. In addition, if you are one of those that really does not cook the brisket by the proper standards of flat tenderness then you are pulling them before they are done enough to mild out.
Second, the problem could be your rub. Now I used large grain rubs.... Not too large like those thick chunks of cracked pepper, but something other than fine. Here is why... and the rule applys to salt as well.... HOWEVER I can think of three restutrants tahtn use a mix like regualr salt, onion powder, fine pepper, medium pepper and ceyenne and do fine.
If the grains are too small you lose control of what is going on the meat. the smaller the surface area the more of anything you can get on the meat before you realize its too much.
And also there could be something else about your process that ****ed the brisket up... for instance I knew one idiot who had a ribbon from one of those KCBS New England pagents and not darn much else that used an injection and the injection was screwing up his rub mojo.
Popdaddy is Dead - 1933-2011 - Pitmaster T is a free agent