I'm a theme park enthusiast. I've been to different parks across the US, Canada, France and Germany as well as the UK.
The two-tier system created by fast passes is a big part of the problem. I see loads of people have already mentioned Europa-Park in Germany, where they do not have this system. It is, without any doubt, the best theme park I have been to. It does not have my favourite ever ride - that's in Florida. But it definitely has the best line-up and experience overall.
It is SO well run, and even on busy days (I've had 4 holidays there, and only ever been at peak times), you will not queue more than about 40 minutes for anything if you watch the queues carefully. It works because it's big, it has lots of filler attractions that are usually walk-on (and these take the pressure off the bigger rides), rides are very well-run with multiple operators getting people in and out, and over the years I've noticed that the same people are working the same rides year after year, which I think makes them super efficient. Without a paid fast track, almost everyone is in the main queue. They do have a limited virtual queue as well, which allows you to bypass the main queue and is free. It doesn't disrupt the main queues all that much because they keep the numbers low.
Food is great there too. It's head and shoulders above any of our UK parks. It is run by the Mack family, who are very good at this sort of thing and make rides for other parks (they built Hyperia at Thorpe Park, and will be building Serpent's Curse, the new water coaster at Paulton's Park).
In the UK, the best theme park in terms of how it's run, queue times and theming is Paulton's Park, in my opinion. But our daughter is 13 now and has been on lots of big rides in Orlando and elsewhere, so she has outgrown Paulton's a bit.
People mentioned the previous 'Fast Pass +' system at Disney. It took a bit of organising but it was quite good because it was free. Prior to that, they used to have machines that churned out paper tickets with a time you could come back to go on the ride. They kept that system longer at Disneyland Paris. But Disney has always felt like it needs military precision to be enjoyed properly, even when 'Fast Pass +' existed. That's why I like Europa-Park so much. You don't need to plan your day precisely. Having been there a number of times, I know I can go on a sold-out day and do everything I want to, and I don't need a spreadsheet or precise plan. It is a bit of a trek but if you do like theme parks I really cannot recommend it highly enough. The food is also great, and good value. They also have two restaurants with Michelin stars if you want to splash out!