There is a thing that happens with 120Hz TVs where they fill in the intermediate frames that the source doesn't have. It's this filling in that is the culprit,

There is a thing that happens with 120Hz TVs where they fill in the intermediate frames that the source doesn't have. It's this filling in that is the culprit, since it's interpolating motion in a way that may not be accurate or realistic, or perhaps that the eye is just not used to, ie. too smooth, or perhaps too averaged.