I spent 10 days here with my son and we had a great time! Stayed in the same building a few years ago, it was a rather slick business hotel, now the atmosphere is very relaxed, more co-working style set up with a very nice young team.
The roof terrace on the 9th floor was mostly unfrequented and allows a fantastic view of Chelsea and the High Line - especially recommended at night. It was very pleasant to relax here in the evening after long rambles through noisier New York areas with a pizza, which you can get from the very good Highline pizza store around the corner.
Room not too big, but everything available, even a small worktable. No problem with WIFI all the time and the friendly staff was very cooperative with any questions. The new Hudson Yards neighborhood with shopping mall and observation deck on the 101st floor is within walking distance and via 3 metro stations you can quickly get anywhere in the city.
There is a nice restaurant on the ground floor but you will also find a number of good restaurants nearby and for the quick hunger several delis on 10th Ave with great selection. A walk to the Hudson River in the evening or a jog there in the morning - you quickly feel at home in Selina Chelsea.