Jackson was really a pretty competent fighter. As I've said in the past, some of his punching technique is really textbook stuff for a power puncher. Usually fairly well balanced, he turned his body with his big punches or stepped in with them to add leverage and weight to the blows, and in some fights he shows very good fundamentals in areas like punching in combination, attacking the body, even using a jab better than you would expect for a big bomber. He was also pretty ****ing relentless if he thought he had an opponent in trouble, although sometimes he could also get overeager and start to be wild instead of sticking with the somewhat methodical approach he adopted after he was too eager and too wild against McCallum in Jackson's first title fight.
His biggest weaknesses to my mind are his vulnerability to speed, (he usually had his feet planted and looking for the big shot, which makes you always a step behind with someone who moves around the ring) a rather average chin combined with an open defense, he wasn't very good at adapting, and of course, the damage he suffered to his eyes. Jackson suffered a detached retina sometime before 1990, and his famous fight with Graham had to be held outside England because the English boxing board didn't want to license Jackson to fight. By the end of his career he had detached retinas in both eyes, according to what I've heard at least, so he really was reliant purely on bombing his opponents out.
One does wonder what might have been if his eyes hadn't been damaged, or if he had been better managed. I was too young to keep up much with the sport back in Jackson's prime, (much less the politics of it) but I kind of feel like the promoters weren't really sure what to do with him, and were content to keep him as an undercard spectacle against overmatched opponents.
Below are some fights that I think do I good job of showing both Jackson's strengths and weaknesses, even during the better stages of his career.