The Club World Cup's various problems have been well documented, from empty seats to storm delays, extreme heat to complaints about FIFA's expanded competition being a cash grab at the expense of the players' long-term health.

However, with the right ingredients slow-cooking in the United States summer sun, there has also been plenty to enjoy about the tournament so far.

Several stars are getting their encore moments, including Inter Miami's cast of ageing former Barcelona greats, led by Lionel Messi.

Now 38, Messi helped the Major League Soccer side make the last 16 against the odds, which coach Javier Mascherano said was "historic".

Messi's mere presence still provokes intense reactions, including from a young boy in an Argentina shirt at the Mercedes-Benz Stadium in Atlanta in tears before the new NBA-style walk-outs, overcome at the prospect of seeing his hero live.

He delivered, too, whipping a superb free-kick into the top corner to earn Miami a shock victory over Porto.

"I'm a Messi fan, he's still one of the best players in the world -- that Porto game we weren't supposed to win," said Yemi Obono, a 34-year-old tech product manager who lives in Atlanta.

He and many others will get another chance to see the forward when Inter Miami face European champions Paris Saint-Germain in Georgia again this weekend in the last 16.

"(Watching Messi) was like a once-in-a-lifetime experience for me... I hope I can go on Sunday and see him again," added Obono.

"I'm happy -- at first I wasn't happy we came second (in the group)."

Messi's reunion with PSG is one of many narratives to catch the eye.

With clubs taking the competition seriously, not least because of the total of $1 billion in prize money on offer, these matches feel "canon", unlike pre-season friendly tours.

"I'm pretty sure for the South American teams, for the Brazilian teams, for Argentinian teams, this competition is maybe the maximum," said Manchester City coach Pep Guardiola, who hailed the passion of the South American fans in particular.

"People are surprised (when) European teams lose," added Guardiola. "Welcome to the real world my friends."

Botafogo stunned PSG in the group stage with a 1-0 win, Chelsea suffered a stinging 3-1 defeat by another Brazilian side in Flamengo, and Diego Simeone's Atletico Madrid were eliminated early.

The group stage has offered some of the tension the revamped UEFA Champions League first round lacked.

The Club World Cup has also offered a first look at Xabi Alonso's Real Madrid project, and new signings like Los Blancos duo Trent Alexander-Arnold and Dean Huijsen, Chelsea's Liam Delap and several Manchester City arrivals.

Coaches including Bayern's Vincent Kompany have appreciated the extra time they have to work in depth with players, swallowed up in the season by recovery sessions amid the packed calendar.

The tournament has been an opportunity to celebrate teams who rarely get to enjoy the global spotlight.

While some mocked New Zealand amateurs Auckland City after their opening 10-0 defeat by Bayern Munich, it highlighted how impressive their 1-1 draw against Boca Juniors was in their final game.

"We're representing 99 percent of club teams in world football who are amateurs... we all have day jobs," said vice-captain Adam Mitchell.

Japanese side Urawa Red Diamonds' fans went toe-to-toe with their River Plate counterparts in creating a superb atmosphere, which is no mean feat.

Although River and Argentine rivals Boca were eliminated, their passionate supporters helped bring the tournament to life.

Even if stadiums are not full, the fans who are there are bringing the noise -- and the average attendance is higher than for La Liga, Serie A and Ligue 1 last season.

Brazilian clubs have flexed their muscles, with all four reaching the last 16, surprising those who thought the gap to Europe's elite was too great.

With the likes of PSG, City, Real and Bayern looking to go deep, some impending blockbuster clashes may yet win over those resistant to the spectacle.

The Club World Cup is a tournament in its infancy, with room to improve, but is already showing it has more heart than some expected.