Should have been one of the greats but drugs took a toll on him. When he was mentally focused he would have been a very hard fighter to beat. Had a style similar to Ali but with more bodypunching and inside skills. He went downhill after his spectacular KO over elite boxer Sumbu Kalambay with half ass performances against former WWs Curry and Starling, slow as molasses Barkley, and eventually a KO loss against James Toney in a fight that he was ahead on the scorecards. He was pretty much a wasted talent. Despite that though he's still a HOF worthy fighter.
I made the Hill comparison because both scored some surprising KOs early in their careers and were considered possible greats-in-the-making, but neither one fully regained their form after their first loss. Although Hill did have continued success at the world class level following the Hearns fight, he never fully regained the speed and explosiveness that he showed earlier in his career IMO. Although Hill had more memorable achievements during his "second career," I believe Nunn was underrated during his. As others have said, his fight with Liles probably could've gone either way, and his loss to Rocchigaini was close as well, although it was a fair decision IMO. In his late 30s, he bombed out a still-dangerous Willie Guthrie up at 175. Roy Jones also concocted some sort of ploy about moving up to HW to avoid a mandatory challenge by Nunn, which I believe could've been a potentially troublesome fight for Jones, though I'd still expect him to win in the end.
He was an elite talent. A 6-2 Southpaw with speed, agility and good boxing skills. Not exactly the guy of guy you want to face. I think his 1 punch KO of Kalambay raised the expectations to an unreasonable level. He wasnt that kind of fighter normally. He landed a perfect punch and some folks thought he was the second coming of Sugar Ray Robinson. There was alot of pressure on him I believe HBO was looking for the next Ray Leonard. He just couldnt handle it outside the ring or in.