Let's put aside any kind of feelings about the movies we may have and let's try to focus on any contradictions that their seems to be between the new movies and old movies.
A couple I have noticed are
1. In A New Hope when Obi Wan first sees Artoo he doesn't seem to have any idea who Artoo is (and C3PO as well for that matter). Yet in the new trilogy we find out that the two droids have been flying around with the crew during the first two (and probably the third movie as well).
2. Also in a New Hope when Obi Wan is telling Luke about his father the way he talks about him would make you think Obi Wan didn't meet Anakin until he was mostly grown already. Yet in the new trilogy we find out that he met Anakin when he was only 9 and had been with him ever since.
3. He also speaks of Anakin as though he was a fellow peer of his and not an understudy and seems to exagerate Anakin's skills from what we have found out really were.
Though the reasons for all this could be at the time Lucas was making the first Star Wars he didn't have in his head what the other movies would be like. But you would think once he did decide to continue on he would make what was described by the characters in a New Hope as a basis for what the other characters would be like.