Like Palpatine and Bail Organa on the balcony at the end of AOTC, did you know the two actors were the only real thing in the shot? Everything (and everyone) else were seperate elements that were composited in. Or the foyer to the opera in ROTS, none of it was there. It's those things that you don't think about that are so well done, it's just amazing to think it started out as a shot of Hayden Christensen climbing up a blue staircase. And I really thought Yoda was leaps and bounds more realistic in ROTS than he was in AOTC. It's a shame, considering this one was the best the Prequels had to offer.
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I do agree that there are some amazing shots that they can do with CG that could have never been done in the OT, but in some ways because of the CG it just doesn't look as real as sets or models. The grand shots of Coruscant of Naboo benefit from CG and make the PT look beautiful sometimes, but I think when you get to the small images, sets work so much better and just look more real.
I was watching SW & ESB the other weekend and then comparing them to the PT movies, at times the PT looks so cartoonish, even though they do a great job of making look almost real, it still doesn't beat using sets. For the space battles between ROTS and ROTJ, I just think the ROTS space battle looks too cartoonish at times too, models are just more believable.
Now monetarily, I know it is cheaper to use CG, and it would be too expensive to shoot the PT with models and sets, but in saving money they sacrificed in the long term the quality of the shot looking more realistic. The OT really holds its worth by just looking more realistic than the PT, just my opinion.