This is a bit of a complicated answer, but bear with me, and I'll try to answer as best I can. Short version is: it depends.

For one, not every gladiator fight was in the Colosseum or another big arena (in fact, most weren't). They had smaller locations in the city for fighting, sort of the equivalent of our minor leagues in baseball. Other Roman towns and cities had their own fight arenas, which generally corresponded to their wealth and size. So as a spectator, it'd vary wildly based on what kind of gladiator fight you were witnessing. Maybe it's something big, with two experts in the largest stadium on earth, with a roaring crowd, or maybe it's a dirt circle lined with stones as a small mob cheers two rookies. For this question, let's assume it's the gladiatorial/chariot racing equivalent of the world cup, some major event in the Colosseum or the Circus Maximus (likely hosted by an emperor, or a notable political figure if it's the Republic). It's far more than just the usual daily or weekly competitions, and will feature the best of the best.

First, we should note the skill and aims of gladiator fights vs football. It's interesting to note that (somewhat paradoxically) gladiators weren't all that great at fighting (or at least, wouldn't use their skill as much in the arena). If you have two highly trained warriors going at it with lethal force, it will be very fast, very nasty, and not particularly entertaining. It's also very hard to see from a distance if you're in an arena. That's why their armor was specifically made to be extra bulky and heavy, why helmets would block their field of vision, why they'd train with exotic and flashy fighting styles. They'd go out of their way to find fighters from every corner of the Empire and show these strange barbarians to the Roman people. That's part of why a surprising number of women fought as gladiators: it was something shocking and interesting for the crowd. It was meant to be a show, along the lines of pro wrestling today. So it's not quite the same as modern footballers, who, despite having some flair and personality, are always expected to be athletes playing an efficient game. If you were to approach one about adding weights to his uniform to make it more cumbersome, he'd look at you like you were a moron.

The treatment of gladiators compared to modern day athletes is... complicated. For one, obviously, gladiators were most often slaves or criminals. They were bound in contract, and were effectively viewed the same way someone might view a prize racehorse. So, obviously, not at all how football teams work today. However, unlike Hollywood would tell you, professional gladiators didn't die often, or even get badly injured. These guys were major investments, nobody is going to throw away three years of expensive training for a five minute fight. While this rule was broken on occasion, fights between two professionals were rarely to the death. They'd have training and workout regimes with specialized instructors, as well as special diets, similar to footballers today. As for how they were viewed by fans, again... complicated. Gladiators were a paradox: the lowest of the low in the social order, but simultaneously cheered and beloved by thousands. This is also potentially an issue with the sources -- some elite romans who form our primary sources looked down on them, but that likely didn't represent popular opinion. We have archaeological evidence of merch (bowls and lamps decorated with them, "I slew my enemies and all I got was this stupid toga", etc.). They were also very popular with the ladies of Rome, and often doubled as prostitutes for wealthy women. I'm not super into football, but I'm pretty sure Messi won't come to my hotel room if I slip him a Benjamin.

But let's get back to the idea of spectators, and what the experience would be like. Such a big event would be advertised ahead of time, and people would flock to see it, arriving at the stadium early for an all day event. In that way, it's certainly easy to draw comparisons to our modern World Cup. And just like the World Cup today, tickets could often become limited (remember, the Colosseum was big, but the population of Rome was way, way bigger). While tickets were technically free and (supposedly) available to all, you could manage to grab some far more easily if you had status or wealth. The elite could go often, while for poorer citizens, it would be a rare treat. Especially similar to the Qatar cup, these days would be used for political gain. You'd be escorted into a dazzling stadium constructed to show the wealth and might of Rome, be given free food, drink and entertainment provided by the Emperor, and generally be impressed by his wealth and generosity.

As you filed in holding your tessara (a ticket, often made of wood or clay), you'd be immediately greeted by an usher. The ticket would have a specific seat stamped on it, and the setup of the Colosseum made it remarkably easy to guide people to their spots. Again, very similar to the World Cup today. Differently than the World Cup (and most modern sporting events), luxury boxes were much further down, rather than being high above the stadium. Since the Romans lacked any TV or jumbotron, the closer you were, the better you could actually see the action.

Unlike the World Cup, where it's the same game with different teams, gladiator spectacles thrived on having a variety of fights. The day would begin with venationes (beast fights, often on horseback), with the most exotic animals they could drag from their homelands. On a major opening like this, at least 5,000 animals would die. Again, a show of power and wealth from the Emperor. This would often have elaborate props and scenery set up, making it seem as if a lion were being stalked through an actual forest.

Around midday, when it got hot, massive awnings would be unfolded to provide shade, and the executions would commence. This wasn't just "Line up and cut off the head", they got creative and sadistic with this. In between the horrific torments, jugglers and other fun acts would keep people entertained.

Finally, in the afternoon, came the big event that people were waiting for. Professional gladiators strode out of a tunnel to a cheering crowd, gleaming with oil. These were the big names, the equivalent of football stars today. It'd take too long to dive into every detail of gladiator combat, but essentially, it thrived on spectacle as well as opposition. Specific gladiators trained in different kinds of combat, and were set against one another, changing up the matches. It wasn't unheard of at the time for people to be fans of a specific type of fighter (retiarius gang for life), and certain gladiators who earned immense fame would be greeted by roars of approval and love from dedicated fans.

Once again similarly to our own modern sports, there were concessions present (chickpeas, bread, wine, etc.). Much of this would be at the Emperor's own expense (bread and circuses baby).

Finally, probably the biggest similarity between sporting events at the time and today was the general spirit and community. Much of the time, people wouldn't be able to see much of the action, or they'd be crammed in close together, but they came just as much for the crowd as for the actual event itself. It was a communal event, one deeply baked into their culture.

​

So, to briefly sum everything up: There were many similarities in how the event was run, how seating was organized, the purposes behind it, and the culture. However, there are also significant distinctions in how the "stars" of each are treated, as well as the actual events that occurred.