I booked one reward night in The Strings expecting that I'd be leaving Tokyo the next day. On check-in I was delighted to hear that my room type had been upgraded (I am a PC Platinum member, but have no Ambassador status). The room was much bigger than I'd expect in Tokyo.
The hotel feels very modern, peaceful, and clean. The view (at least on the rainbow bridge side) of the city and Tokyo Bay is great. I am very impressed with the quality of the hotel and the room. It also made me feel good that the lan and wifi access is complimentary.
Then I was impressed at the flexibility of the staff when my flight plans changed not once but twice. My flight date was pushed back a day, I booked another reward night and the staff was able to make sure that I could keep the same room. Then again my flight was pushed back a day and I had the same positive experience extending my hotel stay for the third reward night.
As for the area - it is very nice that the hotel is so close to Shinagawa station. Shinagawa is a great transportation hub for getting around Tokyo (Yamanote line) and also getting out of Tokyo (shuttle buses, rapid train, etc). It is kind of "business-y" - meaning that Friday after work we saw a ton of people out at eateries and such, but on the weekend it was really calm.
I really hope to be able to come back to the The Strings again in the future!