Sundin is the all time leading scorer for an original 6 team, that's a pretty big accomplishment, and also something not many Europeans have accomplished. He also was the first European drafted as number 1 overall, left Sweden as a teenager, and from that day on was a top-2 scorer for his team during 17 straight seasons. During last 11-12 seasons he was the captain for the team, also something relatively unique for a European born player.
He once had a 30 game point streak, and I think also lots of consecutive games without injury. Lots of game winning goals, and I think tied leader alltime in OT goals. Very consistent. Lots of consecutive 20 goal seasons.
17 straight seasons as a top-2 scorer for his team (13 1st, 4 2nd).
At age 23-36, 13 seasons, he led Toronto in scoring 12 seasons (often goals and/or assists too) out of 13, and once finished a close 2nd behind Mogilny.
At age 19-22, 4 seasons, he led Quebec in scoring once, and finished 2nd 3 times (Sakic and him always being top-2).
No Stanley Cup. But he did prove internationally what a great clutch player he could be, often scoring important goals for the Swedes. He also 3 times was elected to the all star team in tournaments featuring all the best players (Canada Cup, World Cup, Olympics). Several World Championship gold medals, one of those times being voted as tournament's best forward.
Was captain when Sweden won the 2006 Olympics, and assisted on the tournament winning goal.
Definitely could/would have had some Stanley Cups had he played for a better team. (Which may be true for Marcel Dionne, Peter Stastny et al too, but still.)