J + O has a great selection of both 'black and sexy' and 'long and flowery' styles mixed in at a variety of price points. The back is reserved for Top Shop items- well-priced, somewhat decent materials and quality designs.
The front is more expensive, but you can tell a difference in the quality.
I left with one item from the front and one from the back and felt totally satisfied with my purchases.
I wasn't so excited about the customer service here. The change rooms are essentially airport bathroom stalls running along the right wall. There is only one mirror in which you must exit said stall to see how your unique fashion find is fitting. People walking through the store or deciding what to get were always standing in front of the mirror so that nobody could see anything. When I was out of my dressing room looking in the mirror or showing my friend my clothes, I had to tell the same staff person 3 times that 'Yes, that's my dressing room, and Yes, I am still using it." There was a lineup to try on stuff- but only after I had a few items to try in there.
Also, with some of these complicated straps and cuts, I wasn't sure how to wear a few of the things. Nobody was there when I came out to help me get it right, or give advice on what sort of pants to wear with this or what bra to wear with that.
Take a friend, find a sale and go nuts!