First, I want to say that the original film editors of the O-OT -- (that would be Richard Chew, Marcia Lucas, Paul Hirsch, and an uncredited George Lucas for Episode IV, winning an Oscar for their efforts; Paul Hirsch, and an uncredited George & Marcia Lucas for Episode V; Sean Barton, Duwayne Dunham, Marcia Lucas and an uncredited George Lucas for Episode VI) outdid themselves on the theatrical cuts of these movies. Nitpicking aside, I think that the pacing and story imparted through these theatrical edits stands the test of time. To this day, they still rock.
However, after the demise of George & Marcia Lucas's marriage, she would no longer have a hand in anything Star Wars-related, so there's strike one -- and a big strike, if you ask me -- against the prequels: One of the original editors is gone, and sorely missed on many fronts. And concerning the '97 and '04 official re-releases, well, I'm not even touching on how it must feel as an editor (much less director) to have your version of the film re-worked and essentially re-tooled for another generation, and then issued in wide release despite how much money it made and how well it all obviously hung together not so very long before. (Mind you, I do believe in fan-edits, though, so I don't know if that makes me a hypocrite or not...)
Second, and more broadly, the pacing of many movies these days seems geared to the short attention span of the average viewer. Compare the first thirty minutes of Star Wars Episode IV: A New Hope with Star Wars Episode III: Revenge of the Sith. While ANH does begin with a bang, it quickly settles down to the droids on Tatooine, and brings us slowly into the SW universe. It's almost hypnotic. (My nearly 2 1/2 year old son totally loves that part of Star Wars; he excitedly talks of Obi-Wan giving Luke the lightsaber as soon as the old man shows up. But...when I showed my son the opening slam-bam space sequence of ROTS, after several minutes he looked at me imploringly and said, "Watch Star Wars?" See, even the 2 1/2 year old is getting a purist streak.)
I have such a muddle of points beyond that that I'll stop here, because I honestly don't know where to begin breaking down my problems with the prequels. (Mind you, I've not been fortunate enough yet to see any of the great fan edits of the prequels, but I'm hoping that will be fixed soon.)