I never had any illusions about Ozzy, and when The Osbournes hit, it was exactly as I expected. He was just a kid who wanted to be John Lennon, he found some creative (if not particularly talented) musicians to play with, and he did an inhuman amount of drugs. The rest of Black Sabbath never recovered, and what he succeeded with after he left was by virtue of being able to dig up anonymous guitar virtuosos and gifted studio musicians.
It's interesting that the best stuff he did was with the worst musicians he ever played with. As he began playing with more skilled performers (excepting Rhodes) it went downhill. He had a uniquely powerful lyrical delivery, but I think the man's success can be mostly attributed to luck.