Bad fuck: She looks like does not really want to do it, not enjoyment. Too passive, just spreads the legs. Although if she is very hot it is ok. Won't want to do anything, get undressed etc but won't allow you to penetrate her. Also, starts saying stupid things right when you are about to start intercourse. For instance 'I will love you if you go ahead' 'Please do not leave me' that is not the right moment to make those kind of emotional blackmailing. Also, she is on her period and does not prevent you until everything is totally red. For me is a turn off if she starts saying my name like crazy. Also turn off if she makes sounds like she is about to cum continiously but never cums. If she does not cum, is fine but I do get turned off if her sounds are completely missleading.
Good fuck: The girl has passion, erotism, interest in fucking in general, she is playful and has some intuition on how to tease and seduce you. She won't be totally passive (not required to be extremely active unless she wishes too) and understands the flow and mood of the moment. She gets the game.