I am only giving Sanno Byoin 3.5 because of the LONG wait times. The nurses and doctors are courteous & professional with the exception of one male doctor.
Be prepared to wait for up to an hour for an appointment. You should also be prepared to wait up to 30-30 minutes to pay on the 1ST floor and to receive medication.
I find some of the receptionists to be a bit silly and unprofessional at times but it isn't excessively, bad behaviour.
It is EXTREMELY expensive as well.
I've been here a couple of times and I thought the service was amazing. Even without mentioning the grand piano in the hotel like main reception, the staff are friendly and efficient and testing is very thorough. The two different doctors I saw both spoke English - the nurses sometimes cannot. Using Japanese Health Insurance, the (low) price is quite a surprise considering the thoroughness of the examinations. Only downside is that because it's so popular, it can be necessary to wait a while to settle up your account at the end.
I delivered my son here, and it was a wonderful experience. It's expensive, but if you have private insurance, it's doable. (Our US insurance paid all of the cost of delivering at Sanno, probably because an expensive delivery in Japan is still less than giving birth in the US.) It's very luxurious, and the baby, the father, and I all stayed together in the room for the duration of my stay.
If you mention Sanno, people will tell you "Ohh, that's where the celebrities give birth." However, I didn't find it hard to get an appointment or anything, and the doctor seemed readily available. I didn't get an epidural, but they do offer them (assuming you give birth between 9:00 and 5:00!).
During business hours, they have an English translator in the hospital. There levels vary widely-- some fluent, some not so much. But everyone was extremely polite, patient, and willing to speak to me in simple Japanese when I needed it.