This was a great place to stay for an extended trip! It really felt like home the instant we walked in – it had a great scent, a homey yet modern feel, and was immediately welcoming. The location is great, as you are right next to a train station and can also walk to a few major wards. Although it is in busy Shinjuku, it was quite peaceful and restful, away from the noise. You can still hear sirens at night, but I think this is the case for any place in Tokyo.
As other reviews have noted, there isn't much natural sunlight except at a particular time in the late morning, though this wasn't a huge issue for us. The furniture is really beautiful and the lights are warm-toned, so it isn't that noticeable.
Check-in was easy, though the place was quite hard to find when we arrived late at night, as the entrance is in a slightly dark and hidden alley. It would be good to carefully look over and even memorise the instructions provided before you arrive.