Very nice hotel in good location
The One UN offers a lot compared to similarly priced hotels in Midtown East. The rooms and public space are new, pleasant and clean, if a bit coolly sterile (though not W-like). Most if not all rooms have amazing views, since the hotel occupies floors above 25 and there are no surrounding high buildings (the UN and East River are across First Avenue). There is quiet at night, both indoor and outside, which is a rare thing. The beds are comfortable. Like many NY hotels, the TV is big, new and high def, but the cable service is not hi def; however, there are numerous channels and (since the hotel is across from the UN) a few are in languages other than English.
The front desk staff is professional, which is quite welcome compared to several similar NY hotels. The lounge has a small coffee shop and bakery with extended hours, as well as bar and restaurant open late and offering room service. Coffeemakers can be requested for the room, although sadly there are no robes (except undoubtedly in the separate pricier West Tower). The hotel has a pool with lovely view, but limited hours. There are the usual NY amenities within a block or two: coffee shops, small food stores, ATMs, etc.
The drawbacks include one common to many NY hotels: expensive wifi, charged daily and per device. And one not so common: hand-held (European) shower heads only, at least in our room.
It would be nice to see chemical-free soaps/toiletries and (rare to see in any hotel) recycling bins for paper and bottles (though there is the "green" option on linen changes). 
We two adults were given a room that was allegedly an upgrade from the basic king-bed room, and it was very spacious for NY, with a small sofa and a desk, good-size bathroom, large closet and dressing area, and plenty of space for two people to walk around in. It had a nice River view.