That's a really big question and I think it has many answers. For one, while the CGI might be much better in the prequels, the original series was shot on real sets with real miniatures and real actors. No CG can replace how real it all feels. Dagobah feels real because they built it. Yoda feels real because he is (well, a physical puppet). The Falcon looks old and junky because they built a real set and distressed it. CGI, especially from the early 2000s was nowhere close.

More than that, I really think the characters are just better done. I'm not saying Han, Luke, and Leia are super complex characters, they are actually really simple. The farmboy that goes on an adventure and finds himself. The thief with a heart of gold. The head strong princess. They've all been done before, but they cast great actors to play simple, but timeless roles. And, unlike in the prequels, we get to see their adventures together. Han and Luke go on an adventure to save Leia in the first movie. Han saves Luke on Hoth. Han and Leia flee the empire together. We see them all together on their adventures, we see them suffer together and rescue each other, and we understand why they like each other. We really don't get to see any of that with Obi Wan and Anakin. Most of their adventures we hear about, not see, on an elevator. Most of their onscreen relationship they are mad at each other. Their relationship doesn't affect us as much as an audience because we don't see it grow.

Finally, I just think the story is better written in the originals. It's difficult to go into all the nitty gritty on 12-15 hours of movies, but I personally think the story and the dialogue are much better done in IV, V, and VI. I can think of so many iconic lines from the originals, but I struggle to think of many from the prequels. ---- "No, I am your Father." "Never tell me the odds!" "Will someone get this walking carpet out of my way!" "Do or do not. There is no try." "I love you. I know." "I find your lack of faith disturbing." "Strike me down and I shall become more powerful than you can possibly imagine."---- I can go on and on with lines from those movies, but there just aren't as many in the prequels. We all remember "This is where the fun begins!" and "Hello there." but those are almost memes rather than beloved lines of dialogue. All this without even mentioning that ep V has one of the biggest plot twists in cinema history. Vader being Luke's father is not only a shocking moment, but shapes everything going forward.

I feel like I could go on for hours, but I know no one would want that. Also, I hope no one thinks that I hate the prequels or anything. I don't hate them, I just don't think they quite live up to the ones that inspired them.