I think what happens is when we are younger we see movies without contemplating the behind the scenes. We take the stories at face value and we either enjoy them or we don't. As we grow older, we develop more advanced critical faculties, but we never bother to hold our childhood favorites to this higher standard.
To me, the prequels were made with at least as much love and care as the classic trilogy, if not more. I don't understand why suddenly when an actor isn't the best, it's such a huge deal to so many people who had no trouble with Luke in the classic trilogy.
The only difference I can acertain from the many discussions I have had with people who think the prequels are leagues below the classic trilogy is the simple matter of preference.
That the classic trilogy was "good" to you (the good outweighed the bad) and that the prequels weren't so good to you (the bad outwieghed the good).
It's hard for me to relate to it, because to me the prequels are every bit as substantial as the classic trilogy was to me.