Pretty much everyone.
I mean, just look at what he already has achieved, first look at his last (and actually also first) season in the SHL:
SHL Best Junior
SHL Best Plus/Minus (+27)
SHL Forward of the Year
SHL Most Assists by Junior (32)
SHL Most Goals by Junior (24)
SHL Most Goals Playoffs (10)
SHL Most Points (56)
SHL Most Points by Junior (56)
SHL Most Points Playoffs (19)
SHL Most Valuable Player
SHL Playoffs MVP (Stefan Liv Memorial Trophy)
SHL Rookie of the Year
Swedish Forward of the Year
U20 WJC Silver Medal
World Championship Gold Medal
At 19 years of age, he won the SHL regular season scoring title while beating the all time record for points in a season for a junior player (ie under 20) set by Kent "Magic Man" Nilsson in 1975/76!
He had 56 points. The second best player had 54. The second best rookie had 34. The second best junior player had 21.
Also note that Pettersson missed 8 games due to participating in the WJC.
Otherwise he probably would have scored 10 more points, as he averaged 1.27 PPG over the season!
He then went on to win the scoring and the goal scoring titles in the playoffs, of course setting new rookie and junior records in doing so, while leading his team to the championship.
He was named league MVP and playoffs MVP, and of course also best rookie, best junior, best SHL forward and best Swedish forward (the latter usually being awarded to some NHLer).
He won gold at the Swedish and the World championships.
He got silver medals from the WJC and the Champions Hockey League.
Then on to next year.
With 66 points he obliterated the all time points record for a Canucks rookie in the season he turned 20.
The previous record (60 points) was set by 31 year old Ivan Hlinka in 1981 and tied by 21 year old Pavel Bure in 1992.
Not only was did Pettersson score more points than Hlinka and Bure, he was younger then them and he had a higher PPG average; 0.93 for Pettersson compared to 0.83 for Hlinka and 0.92 for Bure.
He made the NHL Allstar Game, as a rookie, and won the Calder Trophy, as best rookie.
And he wowed everyone. Including Gretzky.
At present he has 21 points in 18 games, which would translate to a 95 point pace over 82 games.
Yeah, I think we may be talking generational talent.