Yah, I know exactly what you mean.

With the TPM I was just completely thrown.  The whole movie seemed a waste of time as essentially it simply set up that Anakin was a decent enough kid and that the Sith had returned.  Over 2 hours to convey two fairly basic plot points.  The whole film to me was just irrelevant to the overall story I thought Lucas was trying to tell.  Very cool pod race though.

AOTC was a little better in that there was actually some sense of something going on that could lead to the rise of the Emperor, and at least some hints about Anakin being open for corruption, but it was sunk by some terrible lines/acting plus a general lack of coherence.

ROTS improved things a fair bit, great openning that got lost in the middle but came together for the end.

What struck me at the end of it all was that, ROTS on its own seemed to contain all the plot points necessary, why Anakin got seduced by the Emperor, how the Emperor overcame the Jedi, etc.  TPM and even AOTC both seemed unecessary, particularly TPM, as they contained nothing that really wasn't handled in ROTS anyway.

Unfortunately for ROTS it had to cope with 'that' line, nicking an iconic ending shot from another in the series, the weakest excuse for Obi defeating Anakin I can imagine - 'I have the high ground' - plus of course the worst possible intro of Darth Vader toooooooooo... or is that noooooooo.

Oh well, at least a fair bit of ROTS made some sort of sense and actually worked, plus the duel was killer until it became apparent Lucas had no idea how to end it with victory for Obi when he'd setup the scenario that Anakin was the better swordsman with superior force powers as well.

I know... Anakin's logic was, shall we say, "faulty". It didn't make sense. He seemed on the side of the Jedi right up 'til the end and then suddenly he's all "I'll do whatever you want, my lord" to Palpatine.

That boy really needed a good slap and some Seroquel, Abilify, Zyprexa, Risperdal, Geodon, Haldol, Thorazine, Clozaril, Trilafon, Stelazine, etc. etc... His transformation was way too sudden. Some foreshadowing would have gone a long way there, George.

The high ground part could have been dealt with in so many other ways to make more sense... I just sat there aghast, thinking "dude, he's standing on a small knoll". There were a million other ways Lucas could have gone with that to make it logical. I didn't mind the fight itself because it was showing how Obi-Wan's patience and understanding of the Force balanced Anakin's rage and superior ability, basically neutralizing their overall abilities.

You're right, though. The first two movies were basically filler compared to the last one. Almost everything was explained in Revenge. A more prominent role of Anakin and Palpatine in the first movie and part of the second would have gone a long way toward making things more coherent. Instead, we got the Obi-Wan show which was fine given the rest of the movies because McGregor was the only one who seemed to understand how to act within the confines of the Star Wars universe. Say what you will about the rest of the craptastic performances but Obi-Wan was actually pretty awesome in the prequels.