I was never completely sold on him, even when he was one of the top players for the Oil.
Obviously, the wheels were there. The skillset was good, but the hockey IQ kind of average. Defensively, he was poor, but so was his entire team in that era.
As has been noted, he has an abrasive personality according to some, and at least in his younger days seemed to be kind of dismissive of decorated veterans (famously fought with Andrew Ference in Edmonton; dissed Glenn Anderson in the locker room as a rookie).
Lack of defense and locker-room issues are things that GMs don't find attractive.
Once the Oilers seemed set with McDavid in place, the first thing they did was unload Hall.
18 months after he won the Hart, Jersey unloaded him in mid-season.
Once his contract was up, Arizona didn't offer him anything to stay.
Buffalo (best-run franchise in the League... NOT!) made him a huge offer and signed him. 37 games later... they unloaded him.
He had one good-ish full season in Boston, from which point he has settled into being an unspectacular 2nd liner (3rd liner on strong teams).
I think the best way to describe Hall is that he is (or WAS) an elite-level talent who needs to be positioned as a complimentary player in order to be successful.