Maybe it's harder for older fans to view Star Wars as a "sextet," a complete saga, instead of "two trilogies" or individual movies. I think that is why some people are disappointed with some of the episodes: because they look at it as a competition between individual Star Wars movies, or the old and new movies. Which makes no sense to me, since now we have all the pieces of the puzzle and since Star Wars stooped being a trilogy in 1999. Personally, I think Star Wars is more enjoyable if viewed as one six-part story that has good things and bad things.
If we look at all of the movies in order, we will see that the story is perfectly balanced: Episodes I and II have the exposition, episodes III, IV, and V have the plot, and episode VI has the resolution. Beginning, Development, and Ending.
Having said that, I believe Star Wars has been a sextet since the making of the prequels was announced. But, if someone would put a gun to my head and demanded that I view it as separate movies and that I pick my favorite, in that case, I would put it in the following order from best to less good:
1. Episode V - The Empire Strikes Back2. Episode III - Revenge of the Sith3. Episode IV - A New Hope4. Episode II - Attack of the Clones5. TIE. Episode I - The Phantom Menace and Episode VI - Return of the Jedi
Why the tie? Well, one is not really better than the other one. They have the same weight in the overall story. The only purpose of Episode I is to introduce the characters, and Episode VI's is to tie all the loose ends. Also, I have more love for Gungans then I do for Ewoks, so sue me.