Firstly, this is not Tokyu Stay Shinjuku, we made that mistake and checked in to the wrong hotel initially. It is about 15 to 20mins walk away from the heart of Shinjuku (and its bursting night life). So we had to walk quite a bit to the train stations (nearest was Nishi Shinjuku about 10mins walk) each time we wanted to travel (and inconvenient with luggage).
The room was very small (smallest I have ever stayed) - but that was quite expected in Tokyo I guess and at that price I am not sure if you will get any larger. Bed was comfortable and service was relatively good as they left new towels outside our room when we put a DND sign.
They didn't provide mineral waters (usually complimentary) and no safe deposit box. No frills hotel but just didn't cut it for us.