Warren Savage wrote, "American audiences are 'trained' to look for certain things: full animation (every moving object changes every frame); 'rubberband' animation with a lot of ease-ins, ease-outs and overshoots; exact lip-sync; exaggerated body language and facial expressions; <ADD here list this to>. (I wanted to add the double-bounce walk, but it might not really fit into this list.)
If they don't see these things in sufficient quantity, they seem to judge the animation as being cheaper.
They're not trained to notice: Detailed backgrounds; subtle shifts between background elements to create an illusion of a moving camera; subtle changes in a character's facial expressions (even when a character is shown frozen still and staring at something, the animators will probably animate the glints in his or her eyes); group or crowd scenes with many characters independently animated; subtle character acting; 'camera' dollies, trucks and cranes (these shots take a LOT of time to animate; <.add to this list here>.