The honest answer is that its probably just as good as most whey products out there for all intensive purposes. Biotest may have a couple more goodies in there stuff, but most lifters(myself included) arent failing at their goals because of subperfect whey protein. Instead, focus on price and taste.
And unfortunately, GNC tastes like shit and its more expensive.
Its so bad you laugh everytime you try to down it. Fun, but bad.