I do chalk up the problems to the pupped in Ep I to the way he was lighted. There is a lot of sunlight and bright lights on Yoda in Ep I, whereas in V and VI, he's living in the darkness of Dagobah. The subtleties of lighting can make all the difference in one shot to the next. I just think they tried too damn hard to make the prequels look like something original and not part of the classic trilogy. Apparently they never heard the "if it ain't broke, don't fix it" axiom. Or it's just that Lucas sees cinematic perfection as broke because he can't see the forest for the trees.