Argument 1: The Force is Depressing in the Prequels and the Characters Suck as a Result
In the original trilogy the Force was a much more ethereal thing, a lost art which one could equate to the power of the imagination. Not psychic power, not magic, but pure imagination. It can be bent for great or terrible purposes, used to subjugate and manipulate others or for great good. Most of all, though, those who master it can make great things happen--one needs only to believe in it and in themselves, and to find the discipline to harness it as Luke did. Seeing his journey from a farm boy to the last Jedi Master was deeply inspiring for many people, making them feel as if they, too, could do great things.
Compare to the prequel trilogy. The Force isn't the power of the imagination made manifest, it's not something that anyone can master if they only learn to open their mind and channel it, it's reserved for the privileged; a thing of genetic inheritance that requires people to submit themselves to an elitist boarding school of monks.
Where the Jedi of the original trilogy were deeply in tune with their feelings and with nature, the Jedi of the prequels are a bunch of aristocrats who try to eliminate their emotions, aren't allowed to have relationships, can't have possessions or hobbies, and don't encourage creative potential but rather seek to subjugate it under a strict dogmatic code. Yes, there's reasons for that--but it makes them so in-human that they're impossible to have any interest in, let alone like. They could have put a telekinetic robot onstage in place of Samuel L. Jackson and it would've had the same effect, and that's a horrible waste of Samuel L. Jackson.
Further reinforcing this elitist attitude is the fact that these films focus almost exclusively on the Jedi, suggesting that they're the only ones that matter and that everybody else is just a pawn on their chess board. Apart from Anakin and Obi-Wan, and occasional bits with Mace Windu or Yoda, we just see Padme--and that's only because she's Anakin's love interest; a peripheral aspect to one of those elite.
Compare with the original trilogy, AGAIN, where Princess Leia is a pivotal leader in the fight against the Empire and where the participation of non-force user Han Solo SAVED LUKE'S LIFE on numerous occasions. Not only did the Force seem more special in the wake of all the very outstanding non-force-users in the cast, but these films offered that one didn't necessarily NEED it to be important, whereas the prequels hold that you're basically nothing without it and that it's more important than having healthy, understanding relationships with people.
You see now why these characters are so unbearably difficult to relate to?
Argument 2: There's Such a Thing as Too Much Action
Simply put, the action in the prequels is way too choreographed and sterile. Yes, it's impressive, but outside of a few pauses there's very little expression or emotion in the way the fight scenes flow. They're so busy going through pre-meditated dance steps that're just too damn fast for the eye to see that the actors don't really get a chance to give a performance.
You watch the fight with Darth Maul, you see lots of pretty colors and flips and spins with no really distinct way of telling what direction the fight's actually going in. They're just spinning and spinning and spinning and woops, Qui-Gon's dead.
You watch the fight between Luke and Vader on Cloud City, though, and you feel the dread as Vader repeatedly proves himself to be out of the kid's league, the chill of the wind as he hounds Luke through its tunnels and into the chasms of its airways. It's a better fight because it's much more real and because it's actually moving at a speed that you can keep up with.
Also, the characters are way better established. Compare with the fight against Count Dooku in Episode 2. Count who-ku? The guy just shows up at the end of the second act. We've never seen him before, we don't know who he is or what his motives are, he's just kinda' there throwing out random Sith-ish taunts that don't mean anything. Where A New Hope and The Empire Strikes Back spent a lot of time building up Vader as a threat to the heroes--not to mention their relationships with one another--we just get villains sort of thrown at us out of nowhere in the prequels.
If you're still not buying my argument, though, think of it this way: To create any sense of tension in the final duels of Revenge of the Sith, which is the best of the prequels, Lucas had to do no less than set one in a gigantic arena full of flying saucers for the characters to hurl at each other and set the other on a magma planet with a half-dozen implausible moving setpieces in a river of lava. To create tension in the final duel of Return of the Jedi, all he had to do was put three characters in a quiet, dark throne room. I think that says a LOT about the strength of their respective stories.
