When A New Hope hit the cinemas in 1977, it changed the way special effects would be done forever. Never before had a dogfight between models seemed so life-like. Never before had a model made out of ice-cream stick and scotch tape seemed so imposing. The Empire Strikes Back and Return of the Jedi followed suit, pushing the boundaries of special effects

Enter the prequels, starting with The Phantom Menace. Instead of this B-movie with some props and som models for special effects, Star Wars had turned into a bluescreen and CGI party.

And here's the worst part. The movies are in reversed order! So shouldn't the Original Trilogy be much more visually stunning then the Prequel Trilogy? This fact has annoyed several movie-goers.

Is it wrong? I say no. This is why:

The plot of the prequels are basically surrounded around Coruscant and depicting the fall of the Old Republic. Coruscant is the hub of technology and civilisation. Therefore, being that the plot surrounds Coruscant, we see a lot more stuff that is maybe consider more "civilised" then we did in the Original Trilogy and also these stuff may look a bit sleeker, who says they are better?

The Naboo fighter, however sleek they look aren't as good as for example, the X-Wing.

Also, take a look at the plot of the Original Trilogy. Most of the time it takes place on backwater planets like Tatooine, Dagobah, Yavin, Hoth etc. Hardly the hubs of either technology or civilisation.

And again, just because the stuff in the Prequel trilogy look sleeker, doesn't mean that it's better. The Death Star (I and II) is in the Original Trilogy and is the ultimate of it's time, massive Star Destroyers that aren't even matched during the Clone Wars and the ultimate fighters of the X-Wing and the A-Wing.

The Original Trilogy also displays a kind of Guerilla War and we cannot expect to see the effects there as in the Prequel trilogy. To whine about the CGI being to much and out of continuty is to say that if I made a film about the guerilla warfare during World War II in France and then went back and made a movie about 1920s Paris would be out of continuity.
Trust me. Lucas knew what he was doing.

The Jedi battles are also much faster in the Prequel Trilogy because it takes place during the time the Jedi were at their best and where they had their full training. In the Original Trilogy it's first between and old man and a half-man half-robot. Then between a "not-even" Padawan and a half-man half-robot and lastly a Jedi Knight with not the full training and half-man half-robot. I'm glad that Lucas didn't show Vader fighting in Revenge of the Sith even though fans wanted to see him weild a saber and do cool moves and such as is the spirit of the Prequel Trilogy. Now that would've been out of continuity.

And about the skipping Yoda thing. I don't see why he can't do it. He surely didn't have any reason to do it in The Empire Strikes Back and Return of the Jedi. Seems perfectly allright with me.

Lucas also went back and cleaned up the Original Trilogy making it look a bit better and adding some CGI here and there so that the two parts of the trilogy connected well enough and so that fans wouldn't whine about it all being out of place.

Also, one could argue the fact that Lucas wants to show the Empire being evil by depicting the downfall of civilisation and technology during their rule. The Empire then destroying all of that and the Old Republic being the protector and enforcer of those stuff.

It's up to oneself what one thinks. I think a bit of both, that the plot in the two trilogys are centered around different points and therefore must look different and that the Empire embodies downfall.

Also, keep this Obi-Wan quote from A New Hope in mind when you are dismayed over the use of CGI in the Prequel Trilogy:

It's your father's lightsaber. This is the weapon of a Jedi Knight. Not as clumsy or as random as a blaster, but an elegant weapon for a more civilized age.