See, I always think this kind of opinion is hilarious. Because in my opinion, Episodes 4, 5, and 6 (and I know I may be signing my own death warrant here) are barely above the prequels in terms of quality.

I accept your challenge. Incoming wall of text.

I do think they're better in a lot of ways than the prequels... but when you compare the two sets in terms of cinematic quality, they're really not very far apart.

I disagree in every way that I can possibly disagree.

Completely unnecessary characters that detract from the movie's enjoyment? Ewoks did it way before Jar Jar.

I don't care about the cartoon racist caricature. It was intended to be a funny thing for babies, same as the Ewoks.
What bothers me is the terrible writing, the terrible, flat direction, the lack of focus, the lack of plotting, the fucking everything.

Special effects? Again, good for their time, but...

Special effects are not important unless they are the only thing happening.

The original trilogy was a classic adventure story with some groundbreaking special effects. The 'classic adventure story' was the part that was important. The special effects, as groundbreaking as they were, were always secondary to the plot.

The prequels were a clusterfuck of CGI. Every single scene was shot in front of a greenscreen and it shows - the actors' reactions to things happening is often blunted, muted, because they don't know what they're meant to be reacting to.
The 'classic adventure story' is completely gone. It was CGI setpiece after CGI setpiece after CGI setpiece and in the place of the 'classic adventure' was instead a series of contrivances with no other purpose than to lead to the next CGI setpiece.

It was nothing but special effects.

Acting? Mark Hamill is not much better than Hayden Christensen.

Actually, Hayden Christensen is a significantly better actor than Mark Hamill was at the time, the problem with his performance was that his direction was nonexistent (Lucas is not an 'actor's director' - take a look at any of the Behind The Scenes extras to see exactly what I mean, he treats the actors like they're essentially props to be rearranged on the set) and his dialogue was awful.

Character development? Barely.

Incorrect.

Let's look at Luke and Han versus Anakin and Obi-Wan.

Luke begins as a whiny farmboy who is thrust into a shaky maturity by the end of the New Hope (his family is dead, his new father figure is dead, there's a long and dangerous road ahead of him but he's ready to take it on), learns how to be a Jedi in Empire and by Return is a strong and self-assured hero, a far, far cry from the brat whining to his uncle about power converters.

Han Solo in New Hope goes from a completely selfish scoundrel who only cares about getting paid to nearly sacrificing himself for some kid he barely likes. Throughout Empire he passes up huge opportunities to fuck off and leave the Rebellion to its own fate and shows just how fucking resourceful he actually is and by Return, he's a genuine romantic lead.

Even the friendship between the two of them grows and develops. When Han and Luke first meet, they can barely stand each other. But they go through some serious shit on the Death Star and by the end of the first movie, they're comrades enough that Han actually comes back to flat-out save Luke's ass. Empire begins with Han again outright saving Luke and then, in Return, it's Luke's turn to come back and save Han from the fate Han had been running from since the very beginning.
By that point, they are old friends and act like old friends.
There is no doubt about their relationship, we have watched it develop.

In the prequels, where's the development?
From beginning to end of Phantom, Anakin is a stupid little kid. From beginning to end of both Clones and Sith, he is a whining, selfish, violent murder. He is introduced as a self-obsessed shitflick and never stops being a self-obsessed shitflick. There isn't any development at all.

As for poor fucking Obi, he starts off in Phantom as a good (if bored and boring) impersonation of Alec Guinness as a young man and doesn't fucking move from there. Throughout Clones and Sith he never develops a trace of personality, he just sleepwalks through CGI setpiece after CGI setpiece, bickering endlessly with Anakin the whole entire way.

We never learn anything about either of these characters except that Anakin is unbelievably self-obsessed and Obi is... shit, I cannot even finish that statement, we never learn a single thing about him over three films. By Sith, when he's suddenly smiling and goofing around like a drunken fratboy in the middle of the biggest galactic war ever, it honestly seems like Ewan McGregor has just plain given up. ("Hello there!" he shouts at Grievous after taking ten minutes of screen time to carefully sneak up on him, utterly ruining his element of surprise and putting his entire mission in jeopardy for no fucking reason. This is the same guy who scolds Anakin with the words "Patience! Think!")

As for their relationship with each other, jesus h christ.
We are told they are friends, but we see nothing of their friendship.
Obi-Wan seems constantly annoyed by Anakin and Anakin shit-talks Obi-wan behind his back any chance he can get.
Anakin bleats "It's all Obi-Wan's fault" like a petulant 5-year-old more than once, shrieks that his master is 'holding him back', that 'he's jealous' and never budges from this position.
"Ani was a good friend," says Alec Guinness, wistfully, in A New Hope.
Such a good friend, in fact, that the two of them seem to be a heartbeat from killing each other in every fucking scene they share in the prequels.
Their 'friendship' seems to be based wholly on shared animosity and by the time they finally fight, the only real question is why it took so long for them to GET to this fight.

What about the romantic subplots?
Han and Leia vs Anakin and Amidala?

Same as before, we actually see Han and Leia's relationship develop. In A New Hope, she can barely stand him but again, they go through all kinds of hell together and we can watch their love actually ignite and grow.

By that classic exchange in Empire, ("I love you." "I know.") we have become attached to them as a couple. We want to see them prevail together. And when they are finally together, at the end of Return, it feels triumphant. We have watched their relationship grow and develop and seeing them together, by the end, makes sense.

Amidala and Anakin? And keep in mind, here, Natalie Portman is a great actor - a hundred times better than Carrie Fisher on her best day and it is never remotely apparent what she even sees in him.
She is a democratically elected official and he's a self-obsessed, whining, violent lunatic.
Also he is creepy like a motherfucker and she appears to be an idiot.
He bitches nonstop about Obi-Wan and the Jedi order, mentions flat-out that he supports a fascist dictatorship ("But what if people don't listen?" asks Amidala. "Then they should be made to," replies Anakin.)
and then slaughters a whole mess of women and children and then whines whines whines whines whines and cries about it forever.

Her response to all of the above is to marry him.

See me, if I was her, I'd have gone and told Obi-Wan that his fucking padawan is a crazy psycho murderer person and very fucking obviously firmly on the dark side of everything.
Marrying the whiny shitflick would not have been my first choice, there.

Story? Cool storyline, I guess, but plot holes you could drive a Star Destroyer through.

Plot holes can be overlooked if a story is strong enough.

The Originals had a villain with clear motivations, a clear main character, and an obvious plot progression. It centered around a classic heroic protagonist and followed his arc to a clear conclusion. From Hope to Empire to Jedi, we follow Luke and his friends, we see their plights, their struggles, their triumphs, and we are never confused as to what is going on and why.

The prequels have a villain whose plot is never fully explained and never moves further from there. The first movie does not even have a main character, for fuck's sake.

See, I'm okay with the various plot holes in the originals, because the story is so solid. But the prequels don't have that at all, all they have are a series of CGI setpieces with nothing but convenience to tie them together.

As a result, all it has are plot holes.

Why are the Trade Federation working for this mystery villain? What are they getting out of this, apart from losing thousands of their robots and dozens of their capital ships? It can't be political favors, as that would give Palpatine away. Why are they loyal to him at all, so loyal that at the end, when they are arrested, they NEVER start pointing fingers and mention HEY WE WERE ONLY FOLLOWING ORDERS FROM A SITH LORD!
WTF is going on with the clones? Why are the Jedi taking them in, even though they have hard evidence that they were made in secret by a fallen Jedi and are directly related to a massive plot against the Jedi?
Who the fuck is Grievous and why does the story keep piling on new antagonists without bothering to explain their purpose and motivation?
Why did the Jedi just blithely play right into Palpantine's hands without once stopping to consider HEY YOU KNOW EVERYTHING ABOUT THIS FEELS EXACTLY LIKE A BIG HUGE TRAP?
Is Palpatine just controlling everyone's minds at once?
If so, if he had that kind of power, why bother with all this subterfuge, why not just control everybody's minds to begin with and FORCE them to give him control?
Why did Palpatine consistently make choices that failed to back up his own plans?
For example - and one small example - if, in Phantom Menace, Palpatineis only having the Trade Federation invade Naboo to create a crisis so that he can have himself voted emergency powers, why does he order the Jedi (who are basically only there to witness that crisis) killed in the opening scene? Why didn't he order them sent back to Coruscant with news of the invasion, so that his own fucking plan could happen? I mean, if they actually were killed, how would the Senate even know that a crisis was happening? Seriously, the first thing the Federation does before invading is kill their communications. The only way the Senate hears about it at all is from those same Jedi.
Once again, why, precisely, is Amidala in love with Anakin? Why did she keep his mass murder a secret from Obi-Wan? She's a Senator who has spent time on Coruscant, she knows what the Jedi Council is, Yoda and her are even on a first-name basis ("To see you again brings warm feelings to my heart" says Yoda to Amidala in Attack of the Clones), why the fuck didn't she tell any of them that Anakin totally gave in to anger and murdered women and children?
Why did she act shocked that Anakin would kill "younglings", when she knows for a fact that he ALREADY DID THAT?
Why the fucking fucking fucking hell did Amidala "lose the will to live" shortly after giving birth to twins? One would think "oh, hey, I just had two babies and they totally fucking need me" would be enough reason to keep that there 'will to live', don't you think?
Why are the Jedi totally okay with the existence of slaves on Tatooine?
Why did Anakin never come back for his mother after ten fucking years?
WHY IS ANY OF THIS HAPPENING?)

Everyone just loves them because they came first

No.

Those of us that love them do so because of their strong direction and that aforementioned classic adventure story.

Strong editing, great direction, a decent script, and a lot of people willing to challenge Lucas when something didn't fucking work.

Flash forward 25 years and Lucas is a multibillionaire, the boss of the company and can simply fire anyone who disagrees with him.

Nobody challenges him on anything. He has complete control over everything.

And it shows. The direction of character scenes are flat and lifeless. The action scenes are cluttered, overblown and go on too fucking long. The dialogue is so bad it hurts to listen to and all the actors are directed so blandly, so fucking flat they barely seem to be human.

There is a fucking galaxy of difference between the two trilogies.

Several of them.