"did a reasonable job as president of South Africa."
Well, he brought the country back from the brink of civil war, put a basic welfare state in place where there was none before, and essentially gave the country a new future.
Worldwide is harder to answer because his impact was a more abstract 'leading by example' sort of way. Having displayed compassion and forgiveness in an extremely public position when he could just as easily have chosen the alternative, he gave the world an exemplar statesman. A lot of his worldwide impact was essentially how other people chose to perceive him and honour his achievements than anything he actively did.
I agree though, I don't really the gushing-ness of the tributes to him that are coming out.