Exceeded my very high expectations
I was spending time in NYC on my own and was looking for somewhere I would feel comfortable. I realy liked the reviews for the Library Hotel and it's location was also perfect for me. 
Most of what I liked about the hotel has already been mentioned but I want to add that the Library Hotel is ideal for solo travellers as you are made to feel so welcome and all the staff are friendly (and genuinely so rather than putting on an act) and helpful. 
I have seen a review which complained about the time taken for a bell boy to find a cab - I watched from the window as one bell boy stood on Madison Avenue for over 10 minutes putting his life at risk as he walked in front of traffic to try and hail a cab. It isn't the hotel's fault that free cabs are so difficult to find.
I am already planning my return visit.