i think as a whole the films are very good, exciting and enjoyable to watch.
on the question of if it is a good depiction of a Dom/sub relationship (as a whole) id say no for 2 reasons.
the billionaire fantasy land thing shrouds everthing else and the fact that instead of just being a normmal controlling Dom character, they decided to go with the typical over-done and unoriginal "what made him this way" routine probably because its easier to milk a 3-film story with damaged childhood backstory.
i guess they are the bad parts so here are the good.
there are some incredible scenes that in my oppinion display power exchange perfectly and really put you in the mind of the characters.
the soundtrack is amazing.
i think the main character is great, how she develops over time is really what its all about.
i like the casting too