I had a good experience at the Interfaith Guest House. It may not be for everyone though. The rooms are extremely small, thin walls and no sound barrier ceiling. There was no hot water to shower on my second day (I think this was an isolated incident), but thankfully I don't mind quick cold showers.
The fresh fruit, nuts, etc. that are provided throughout the day was a nice amenity. I was concerned about the noise based on some other reviews, however, everyone was very respectful of keeping a library like environment during quiet hours. And even outside of the quiet hours, it was always peaceful. If you're a light sleeper, do bring earplugs or earphones as you might hear people moving around especially late/early arrivals/departures of other guests.
I also took advantage of the invitation to volunteer with their food service program. This was by far the highlight of my stay. I helped prepare the meal at their kitchen facility in the East Village and then we loaded everything up and went to Tompkins Park where we served around 125 people. We served every ounce of food. And while I didn't have an opportunity to try the food, everything looked amazing and was prepared very professionally. Total time takes about 2.5 hrs.