The Broad Street Bullies played a style built around physical play and defense. They were heart and determination, not speed and skill. The Flyers were not an aesthetically-pleasing team in any way, whether it be their style of play or the toothless face of the organization. They were the red-headed step child of a league that preferred it's public image to be that of one of it's older, more handsome, and more polite children. There were only three teams that won the Stanley Cup during the 1970's. The Broad Street Bullies were the antithesis of Bobby Orr's Boston Bruins and Guy Lafleur's Montreal Canadiens. They were that third team, the miscreant in a group with two golden boys.
The 1974 and 1975 Stanley Cup Finals were the ultimate showcase for the two dominant contrasting styles in the NHL. It was the speed, skill, and skating against physicality and defense. In 1974, the Flyers were supposed to be crushed by Boston Bruins, who featured the top four scorers in the league, including a 25-year old Bobby Orr and a Hart-winning Phil Esposito. The Bruins had scored 73 more goals than the Flyers in the regular season. Bobby was the dominant player in the Finals. But it was the wrong Bobby, the one everyone forgot about. The Flyers got physical with Orr, with Bobby Clarke leading the charge. Orr was neutralized (for his standard), and Bernie Parent took care of everything else. The next year, Philadelphia avoided both Boston and Montreal en route to the Cup Finals, and faced a highly-skilled Buffalo Sabres team led by the French Connection. Just like Boston the year before, the powerful Sabres' offense vanished against Clarke, Parent, and company.
The immortality of the Broad Street Bullies is not a result of their style of play by itself. Maybe they were goons". But they were "goons" that played outstanding team defense and proved that the combination of physicality, defense, and Bernie Parent could shut down anyone. They proved that they could sustain that type of style long-term. That is why they are special.