I personally don't have a problem with CG in general. I think as well that it is definitely a helpful tool in the creation of movies and creatures that wouldn't have been possible with traditional methods. What I do have a problem with is directors thinking that they should use CG because they can and/or use it so much to the extent that it becomes style over content.
It's the overuse and misuse of CG that is a determining factor (not the sole one as you might have read :-) ) in my dislike of the prequels.
In the original trilogy there are many SFX shots and they have shown their age. However, unlike the new ones, 99.9% of the film is not a constent special effect. Had every background been a matte shot, every alien creature a "cartoon", had every piece of fruit been an animation, the film would appear to be very fragmented, dull and fake right? Imagine if the whole film looked like that scene when Luke and Han are talking on the barge on their way to the Scarlac? Wouldn't that have been...well, really cheesy? That's how I feel with the special effects in these new films. Everything is a special effect and because of that decision, the whole film will age...badly.