Different perspectives on what makes a good park is obviously the first point, I also think everyone had really high expectations and some it didn't match them
I haven't been yet (will in a few months), but I will echo what I saw Defunctland say on his charity stream in December: "Epic Universe is definitely not the best theme park in Florida, but it's the best start to one"
Please remember that even Disneyland, one of the most celebrated parks in our community, was not very good when it opened. I think that Epic Universe has everything it needs to become Universal's new flagship and many probably see that, others see that it did not deliver quite the heights that they feel Universal could have reached given both how it has been talked about + what they've seen the company is capable of when they really lock in. Many of the attractions there now are not going to stay though, things change and update over time
That said, I could also go and completely disagree with everything I just said. This is an observer's perspective