I did not like this experience. I will say that I stayed in another capsule hotel in Tokyo and this one was MUCH better, it still wasnt great. The location is great for shopping and hitting up the fish market in the morning. The employees were really nice and the facilities were okay. As a woman I felt safe there because of the card access security.
So those were the good things. The bad things were that it smelled really bad in the sleeping quarters and there is no air flow in the cabins, so the smell just lingers. Unless you're on a tight budget (and can't afford anything else), or so drunk you'll pass out not knowing, then I would skip this unique Japan expreience and instead get a good night's sleep in a real hotel.

Affordable stay for the location, which is minutes away from Tsukiji Market. Easily reachable from either Narita or Haneda Airport by the Asakusa train line via Higashi-Ginza station. Also less than two minutes’ walk from Tsukiji station of the Hibiya metro line.
Clean bathrooms with toiletry and laundry machines, individual private showers and communal Japanese-style baths, separated by gender. Unfortunately, their mattresses are very firm and can feel uncomfortable to some people. Noise may be an issue in the morning or at night due to other guests.

Had one night stay in Feb this year and was totally satisfied with the room and the facilities. It is not a typical capsule but a room without ensuite bathroom. The whole place is well maintained and clean. It was quite occupied for a friday night and I could hear some snoring in between the whole night but it is not a big issue for me.