I've always thought that if Episode I had been better received critically, II and III would have been very different, I really get the feeling that whatever he had planned changed after Episode I.
Would they be better movies? I don't know, but at least on Episode I he tried some new things and some new designs. It's like he said "Oh, they didn't like it, whatever, let's just put Boba Fett, Stormtroopers, Star Destroyers, asteroid fields, ships that look like X-Wings, walkers, speeder bikes, ships that look like TIEs and the Emperor's Throne Room from Jedi in the next two movies". And I do think that Episode I, as bad as some parts are, is by far the best of the prequels. Probably because he shot it at locations and real sets for the most part.