I have always wondered this, and living in South Florida, there is a common thought process...whatever the Tuna does, it is good. 
Here are his numbers: 

• Regular season: 172-130-1 (0.569)
• Playoffs: 11-8 - 2 Super Bowl Rings with the Giants

Compare those to say, Bill Cowher:

• Regular Season: 149-91-1 (0.623)
• Playoffs: 12-9 - 1 Super Bowl Ring

Each spawned many NFL head coaches, but only a few were successful. Parcells is of course known for Bill Belichick, who has in his own right spawned many, many coaches. Personally, assistants who become head coaches is not really a worthwhile measuring stick. 

I guess the big thing about Parcells is that he "turns" things around. When he came to Miami, the Dolphins had just finished a 1-15 season. He cleaned house, brought in 20 no name free agents, and drafted Jake Long with the #1 pick and Chad Henne . The rest of that class has not really done too much, and I for one, don't think the Dolphins will finish better than 8-8 this year, although I may re-think that prediction. 

The Cowboys: Do I even need to rehash that part of his career? In fairness, he was working for Jerry Jones who is a delusional ego maniac who thinks he channels the football genius of Vince Lombardi and Nute Rockney combined. Still, his record there: 34-30, 2 wild card playoff appearances and 2 losses. 

The Jet years: 29-19. He inherited a 1-15 team. They were in the playoffs two years later, making it to the AFC Championship. Next season, they went 8-8 and he left for retirement after one more year as GM where the Jets finished 9-7 and out of the playoffs. 

The Patriots: 32-32. A Super Bowl loss, and one other playoff wild card loss. In 1993, he took over for a, yes, 2-14 team. In 2 years the team was in the playoffs, had a terrible season, then made it to the Super Bowl, losing to the Packers.

Yes, I get that he took over for teams that were terrible, and made them winning franchises, but how do we define winning? Making it as wild cards, division titles, Super Bowl appearances or Lombardis? 

Using the Cowher example, he took over for a 7-9 team. Hardly devoid of talent to be fair. Yet Cowher won the division 5 out of the first 6 years in Pittsburgh...making the playoffs all 6. Then we had the dark ages, 3 straight years with no playoffs, followed by another run of 4 out of the next 5 years, culminating with the SB XL. In those 4 playoff years, the Steelers won the division 3 times. The only wild card, they went on to be the first 6th seed to win it all. 

So, is the allure that he is Mr. Magic Turn Around Guy? Or is he a pretty damn smart guy and take jobs that he knows he can work his magic. Could he do the same with say, the St. Louis Rams or Cleveland Browns? I doubt it, those teams need a lot of help. The Raiders? Certainly, as long as you could get Al Davis thrown in the loony bin for his JaMarcus Experiment and bring in even an average QB (With Garcia, I bet the Raiders could have been 0.500 or darn close). Now, the team is lost and just does not care. 

As we often point out here, football is an extremely complex game. It takes so much to build a winning franchise. It is why organizations like Pittsburgh, Philly and New England are praised for putting competitive teams on the field every year, even in the salary cap era. You need the right coaches, the right players, the right leaders and then you need some luck...no injuries, the right bounces, etc. 

Parcells likes familiarity, and often brings in those who have worked under him in the past, coaches or assistants, or players. Remember the Cowboys and Bledsoe, Glenn, Keyshawn, etc. 

Since the NFL realignment, we know how schedules can affect parity. There are definite "weak" divisions, and strong ones. A 1-15 team, like the Dolphins, who get to play the "weak" divisions, and two last place teams, can have incredible rebound season. What the Dolphins do this season will either add or temper his legacy in my opinion. I can't see the Tuna hanging around much longer down here, with the ownership looking like some bad latin-pop festival. Anyone with a spare million can buy a minority interest in this team. Is it worth having this guy come in and do things his way, get a year of success (albeit marginal if your goal is to win it all) and then see him "retire." 

Anyway, please, give me some opinions on where you see Parcells in the list of coaches and GM's. It just seems like the media just gushes over this guy, who again, is certainly a good coach, but I just think the level he is placed on is not really deserving. I'd like to hear from the fans of those teams who experienced the "turnarounds" and what he accomplished, and what it was like pre- and post- Tuna.