Location not everything
6 Columbus is a fantastic location if you wish to be near Columbus Circle and the lower part of the Upper West Side. But that is the only positive thing I can say about this hotel.
My wife and I stayed at the hotel for two nights in mid September. I am amazed that there are positive reviews on Tripadvisor. It does seem that the hotel draws either very positive or very negative reviews. My view is firmly negative.
The hotel is in an old building - presumably a converted old hotel. It should not be considered a new hotel. Thompson seem to have kept all of the narrow corridors and small spaces. It reminded me of the inside of a two star hotel in Paris. Poorly laid out and cramped. There is one normal size lift and then a tiny lift the size of a cupboard. The colors are all dark and the place looks rather cheap.
We stayed in a king room the room was still very small - even by New York standards. There was no where to put the luggage bags and the only seat faced the door to the room. You could walk around the bed but there was no other space. The bathroom was very small and the shower was in the bath. The bath has to be the narrowest bath I have ever seen and it was an effort to not continuously stand on the plug. The bath was no narrow that your feet were partly on the curved sides.
We woke up one morning to no running water in the room. Apparently there were water pressure problems on the upper floors. It was fixed a few hours later. But I think it shows the limited job which has been done by Thompson to create this hotel.
The bed was comfortable - nice linen.
There was only a curtain across the window - no sheer, so you had to have the room in darkness or the people in the adjacent building could see in.
The room was poorly appointed. The only toiletries were soap and shampoo. No conditioner or body lotion. No ironing board. my wife could not believe the tiny hair dryer.
Our room seemed tired even though the hotel is new. It did not appear to be particularly clean. There were several marks on the furniture and one light bulb was out. The air conditioning was very noisy.
When I checked out I had to ask if the desk person was going to ask how my stay was. She seemed surprised when I told her how disappointing it was. 
I have stayed in other boutique New York hotels like The London and The Crosby Street hotel and 6 Columbus is a poor comparison. It is not worth $400 per night. It's rooms are tiny and the building is cramped. I would not recommend it. In hindsight, I should have more carefully looked at the website photos - tiny rooms with basic furnishings and a tiny lobby. Not good signs.