Williams retired from international rugby at the back end of last year and will hang up his boots altogether when the current season comes to an end.
As a double Grand Slam winner, the record try scorer in Welsh international rugby, the first Welshman to be crowned the world's player of the year and a Test Lion, Williams has done it all.
And now his former regional colleague and current coach has sung his praises ahead of what will definitely be his final game at the Liberty Stadium unless the Ospreys secure a home play-off semi-final in the RaboDirect PRO12.
"I don't think there's been anyone better than him - ever," said Humphreys.
"You don't often get a kid who has that much skill and gas and can back it up with a ton of guts.
"I remember thinking he would never make it when I saw him playing as a kid coming through - he looked too small. But he's proved everyone wrong to be one of the best finishers in the game.
"All the superlatives have been used up for him. He's been unbelievable."
Williams ended his Wales career in style when he scored his 60th Test try (58 for Wales and two for the Lions) with the final play of the game against the Wallabies in December.
And now Humphreys is hoping for a similar scenario at what could be the star wing's last hoorah in Swansea as he looks to end an Ospreys try-drought that dates back to October 2010.
"Suffice to say this group would love to see Shane go out with a bang because he's been absolutely huge for us," added Humphreys.
"He's been a pleasure to watch and you only have to consider the impact he's had as a world player of the year playing for this region, coming from this region and wanting to finish his career here.
"It's a massive occasion, with Shane playing what could be his last game in Swansea. He's a huge member of this squad and we want to give him the best send-off we can.
"We want to make sure we mark his finishing by giving the kid the respect he deserves."