I haven't studied extensively, but have done a few seminars and worked out with Rolier Gracie....
GJJ is a great on ground defense against one person. It's extremely limited. But any good martial art out there can make you a better person, or a bigger arsehole. I'll leave it up to you to figure out which one it'll be
getting ready to take brazilain jujitsu and just wondering how big of a differance is it
Difference as compared to what? I studied Judo under my father who earned his black belt in Japan under the venerable Mr. Eto 10th Dan. As part of learning the sport of Judo there are also lessons in self defense or goshin jujutsu which includes things like eye poking and hair pulling in a manner of self defence. Judo and Aikido are designed to not injure your opponent where the sport of Brazilian jujutsu looks kind of brutal. Thats one difference at least from the origins of jujutsu and judo. Jujutsu did not evolve from judo per se but Judo is a basic form of jujutsu so you would find it to be very different from Karate as it still emphasizes holding and locking the joints.