I saw his last fight and liked it, so I've spent some time watching 5 or 6 of his fights, to educate myself. how good he is, it is hard to tell because the guys he fights are so, so, so bad. Plus, a lot of them a lefties and that is always a weirdness factor. most guys that fight southpaw do it because they are too lazy to learn how to fight- we'll debate that at another time- so it always skews things when you watch.
GGG has some funky habits. He raises his elbows when he jabs and throws his right hand- no straight punches, that I've seen, everything arcs. When he throws his right hand, he often brings his right foot forward; I thought he did it only with southpaws but he does it pretty regularly. This gets you timed and knocked out- watch botha vs Tyson and moorer to see how you counter this with your own right hand. he stays in range to much, catching punches, though in some fights he got out of reach pretty quickly.(this is how you control distance-and how you avoid telegraphing your moves).
The idea of him fighting with a Hopkins, Toney, Nunn, Hagler, etc..at 160 is pretty far fetched, laughable. If he had been fighting the guys that hagler fought, the monroes and Watts, etc... he'd be 16-4, but he'd be a much better fighter than he is now. I think he can learn buty i don't think the guys he is fighting can teach anybody anything