I have a particularily strong dislike for the lack of visual continuity between the OT & PT.
Now, I'm not talking about the shiny-vs-used-universe thing or even how technology in the PT looks more advanced than technology in the OT; I'm talking about how things which appear in both trilogies -- Obi-Wan and Anakin's lightsabers, the Tantive IV, Vader's armour, etc. -- don't match up on a visual level.