Anytime I look up this movie in a review book or movie website, all it usually says is "Rocky defends his belt against Mr. T. Stallone can milk the formula but it's time to move on." I always like to think that what was written about this movie is what was written at the time, which it probably was and that it really needs another look especially after Rocky's IV and V came out.
After winning the championship from Apollo in Rocky II, Rocky's life is now kicked into high gear, he's defended his title 10 times and has started doing charity work, and numerous commercial endorsements and is making money. Along comes Clubber Lang a loudmouthed lump of muscle wants some of Rocky's action and even exposes that Rocky has been fighting safe opponents to hold onto his title. Infuriated, Rocky wants to take him on, but Mickey tells him not to since Clubber would destroy him in a match and admits to Rocky that Mickey has picked his opponents to protect Rocky. Rocky implores Mickey to help him train but success has made him fat and we don't see him take training serious. Come match time, no matter how hard he tries, Rocky is quickly defeated and worse yet a heartattack claims Mickey's life. Seemingly feeling defeated, Apollo steps forward and offers to retrain Rocky and get his edge back to win back his belt.
This is arguably also the most action packed of the Rocky movies. 
After the recap bout from Rocky II at the beginning, we have a sequence of Rocky winning bout by bout and defending his title alongside Clubber Lang's victories. Later we see Rocky at a charity event where he takes on Thunderlips, a wrestler which quickly goes out of control. We get two bouts between Clubber and Rocky.
The boxing scenes in this movie are pretty far removed from real boxing though. Rocky's punches sound like cinder blocks being dropped on a sidewalk and Clubber seemed to have taken Rocky's "learn to block punches with your face" class.
Some people never put together the nuances of this movie other then it's ramped up action and what seems like a recycled story. The biggest point I think people miss is being once your on top, how do you stay on top? When your hunger dies for competition is it time to hang it up or do you in fact keep moving? Before the final match the commentators state that it's Rocky's pshcyological damage that could prevent him from winning his belt back. Which damage is that? The fight commentators for the match on TV cites Clubber's ferocity in the ring but what about Mickey dying? Must not have been sexy enough to say out loud before the fight. What about Rocky's self doubt about not feeling like the man he once did when he learns that his past victories were over second rate boxers? Did he completely overcome it after talking to Adrian for inspiration while retraining? I think this movie is a little deeper then some people give it credit for and the carnie aspects of it drive people away. (Think about it, Rocky fights Mr. T and Hulk Hogan who within the couple years after the movie were both at the premiere Wrestlemania.) But it's also the best of the Rocky movies after the first and final ones.
Best of all, this movie has some great lines. The charity match with Thunderlips has Rocky asking how much he thinks Thunderlips eats, with Mickey telling Rocky "about 202 pounds." Within seconds, Rocky hears his weight announced. Guess how much he weighs. Apollo's got a nice tough love line to Rocky when Rocky needs motivation for training and it could be my favorite line in the movie.
Finally, Rocky who looked a little intimidated at the start of his first match with Clubber Lang is a completely new person in the second match. Clubber taunts Rocky:
"I'm gonna bust you up!!"
Rocky without missing a beat:
"Go for it."
Rocky III may not have the same kind of heart as the first film or Rocky Balboa but it has a heart all it's own. Let me make one more reason why this movie rocks. If you've ever been bullied in your life, and couldn't fight back, watching Rocky have the courage to get up off the canvas and knock big bully Clubber Lang on his sorry ass is one of the most satisfying things I've ever seen.
