McClellin spent 2016 and 2017 with the Patriots after playing his first four NFL seasons with the Chicago Bears. He said his time on the Belichick-coached teams were "the best two years of my football career that I've had."
"I definitely think it starts from the top, Bill [Belichick] and Mr. [Robert] Kraft, and then it just trickles down," McClellin told ESPN. "Then you have leaders like Tom [Brady] and Matt [Slater] and Dev [Devin McCourty] -- the captains. When you come in as a new guy or a young guy, and you see how laid-back and easy-going the captains are, they'll just come up and talk to you and genuinely want to know about how you're doing and how your life is. I think that's something that makes the chemistry and camaraderie that much better. When the older guys really care about you, it makes you want to play for them and for your teammates, and not just for yourself."
McClellin, who was a first-round pick by the Bears in 2012, was released by the Patriots with a failed physical designation in March after missing all of the 2017 season.
He said it's difficult for outsiders -- like Philadelphia Eagles offensive lineman Lane Johnson and Brandon Brooks -- to understand the Patriots' way of conducting business unless they've experienced it themselves.
"I would say a lot of guys don't know what they're talking about, because they haven't experienced it," McClellin said. "When you have a winning culture, everyone is going to hate on it. That's what comes with it, it's the way it is. It's hard for someone who hasn't been in the situation to say, 'Oh, it's like this, it's like that.' It's a winning culture and you're going to get slander and hate -- that's just the way it is. From my standpoint, I absolutely enjoyed my time there -- from the coaches to the owners, players and trainers."
Johnson and San Francisco 49ers defensive end Cassius Marsh have criticized the Patriots in recent weeks. Johnson called New England a "fear-based organization" while Marsh said that he "wanted to get waived" by the Patriots in 2017 because "they don't have fun there" and "there's nothing fun about it."
"I was under the same regime in Houston [with O'Brien]. I almost retired. [Expletive] was miserable, every day. Every day," Brooks told Bleeding Green Nation.
O'Brien was an offensive assistant with the Patriots from 2007-11 and became the Texans' head coach in 2014.
"I came in [as a rookie] under [Gary] Kubiak, who was just an older version of Doug [Pederson, Eagles coach]," Brooks said. "Then I went to O'Brien, who was Belichick, and then I came back to Doug, who's like Kubes, so for me, man, [expletive] was great. Like, I cannot tell you how much better this is than it was down there. Like, it's just night and day."
Brooks said that Reggie Wayne's short-lived comeback attempt with New England in 2015 came to an abrupt end because of his displeasure with the "Patriot Way."
Wayne, however, refuted that notion.
"There are some reports out there that I left New England because I said it was not fun or it was too hard," Wayne told the NFL Network. "Those reports are false. The fact is, I was done. It was time for me to retire. There were other teams that wanted my services but I knew it was done for me."
Wayne played 14 seasons with the Indianapolis Colts, earning Pro Bowl honors six times and finishing his standout career with 1,070 receptions -- 10th on the all-time NFL receptions list.
Belichick, who has guided the Patriots to eight Super Bowl appearances and won five championships, was not interested in how other teams go about their routines.
"Yeah, we're focused on what we're doing, trying to get better and taking each day we can to try to improve our football team," Belichick said last week. "Not really focused on what everybody else is doing."