As someone who lives a BDSM-heavily centered lifestyle, 50 Shades of Grey is a poorly written book which features a psychopathic, sadistic stalker who charades himself as a "dominant" male who does not understand the core beliefs the BDSM community has tried to make clear - consent is clear, aftercare is important and communication is an absolute necessity. 50 shades is another great example of Hollywood glorifying domestic violence under the guise of romance.
Dungeon scenes should be discussed in-depth and impact place preformed by people who know what they're doing... untrained Dom/Dommes hitting you in the right place multiple times can cause organ damage, permanent scarring and other injuries.
BDSM is something that is very personal and close to my heart and seeing it displayed in a way where people are romanticizing an abusive relationship and calling it "kink" makes my heart sink. Even though people are smart enough to separate a book and reality, the ideas that perpetuate violence within relationships and making it seem acceptable are very apparent in these books.
Just my 25 cents