Sharp delineations are lost. Edges become softer, and objects with a range of colors (light brown to dark brown) have "bands" of colors, rather than a gradual change.
I think the smoothing effect and loss of detail during motion bugs me the most. Just look at the carbon freezing scene in ESB in any of the bootlegs. It looks like the characters are being attacked by ghosts instead of surrounded in steam. I'm hoping a high-bitrate DL version will improve upon this.