When they were at their best, playing against Pep Guardiola's Barcelona could be a soul-destroying experience, and I should know: I played in two Champions League finals against them and lost both.
It was not only the fact we lost a European Cup final, although that still hurts, it was also that at times you did not feel you were in a position to do the things that came naturally as a Manchester United footballer. By that I mean having plenty of the possession in a game, setting the tempo and controlling the match. When you played Barcelona, they did all that themselves.
Even when we beat Barcelona in the 2008 Champions League semi-final second leg at Old Trafford, my main memory of the game - the goal aside - was that they had possession for long periods. We did not go toe-to-toe with them, but instead contained them as best we could and defended our lead.
In that era Barcelona were special. They were undoubtedly the best team in the world and so I was interested to see them in person this season with that attacking combination of Lionel Messi, Luis Suarez and Neymar.
I went to see them play away at the Mestalla on Sunday with my old team-mate Phil Neville, as guests of Peter Lim, who owns Valencia and has an investment with us in Salford City.
I watch Barça as much as I can on television, and this was just a snapshot of their season so far, but for much of the game I felt they were a ghost of the side they had once been. They still pass the ball relentlessly, but that old drive and tempo are not nearly as urgent. The breathtaking speed and penetration have gone. They won the game in injury time but even in those final stages, they hardly created chances.
When I try to find a way of summarising the attitude of the team, and of some longer-serving individuals, I keep alighting on the word "bored". It is not meant to sound flippant, but it just seems the most accurate way to describe the way the team seem to treat the style of football that once made them the best team on the planet. The midfield on Sunday was Xavi, Javier Mascherano and Sergio Busquets.
This was not one of Barcelona's finest days, one in which Luis Suarez struggled and Neymar looked a bit lightweight. At right-back, Dani Alves seemed to be under the impression he did not have any defensive role to play. Valencia were well-organised and they should have won the game.
To put it in context, Barcelona have dropped only eight points in the league this season and they are second, just two points behind Real Madrid. But in terms of the way they are playing it feels like something is missing.
As for Messi himself, his achievements put him in a different category to the rest of us who played the game. But even so, in him, as much anyone, I detected that mood of boredom. He has never been a player given to chasing the full-back when his team lose the ball, but now, more than ever, he keeps his movement to an absolute minimum.
For a young manager like Luis Enrique, it will be hard to change the way Messi, and the rest of the stars in this team, play the game. They have won it all. They have conquered the world. Now Enrique has to find a way of persuading them to do it all over again, on his terms. You could see him on the touchline trying, and largely failing, to get them to play with greater urgency.
It made me think about the great years at United and how we, as a team, would pick ourselves up year after year. First of all there was our manager, Sir Alex Ferguson, who would push us on. Also, as a United player, you always feared the summer arrivals in the transfer market and how they might affect your place in the team. I can see the parallels between United without Ferguson and Barcelona without Guardiola.
When we came back for pre-season in late July 2009, you could sense that Sir Alex was still angry even then about the defeat to Barcelona in the final in Rome two months earlier. There were always matches to win, targets to achieve.
Watching Barcelona, albeit just one game, I felt that the era of the great team Guardiola built was coming to an end. That does not mean some of those players will not go on to be part of another great side, just that they need to find another way of playing. The game moves on and Real Madrid and Bayern Munich have found new ways of playing, especially against Barcelona.
There would have been more Champions League triumphs for United were it not for Barcelona. I do not begrudge them their success. They were a wonderful team. I just wonder if they need a new direction if they are to hit those heights again.