Yes, Episode III has it's glaring errors. Yes, the dialogue is bad in places. Yes, Lucas's love scenes between Padme and Anakin are not convincing. But I still liked it. A lot. This is the first reviewer I've read who captured what I was trying to say below:
What makes the failure of the first two films so glaring, now, is that with Revenge of the Sith Lucas has finally again tapped into the inspiration of the original trilogy, and created the mythic precursor that he first conceived decades ago. Perhaps he really only had one real Star Wars prequel in him, and didn’t know how to properly set it up with the first two episodes. ...
Yet, crippled as he is by the decisions of the first two films, Lucas still manages to invest the final chapter of his sprawling space opera with the grandly operatic spirit of the original trilogy. It’s still cornball, yes, and with all the usual weaknesses. But Episode III at last has heart.
Revenge of the Sith is the first of the prequels that echoes elements in the original trilogy in such a way as to enhance the original films.