I stayed at The Strings in May 2012 on a business travel. The hotel itself is great, rooms are extremely clean and spacious (for Japan standards the size is very good), nice views, internet speed is outstanding, toiletry is high quality and I can keep going.
Breakfest was very good and it's served in the lobby area.
It's very close to Shinagawa station, so you can get to virtually everywhere within Tokyo.
I know this hotel is expensive, fortunately in my case, the company paid for it, but I assure that it is well worth it.
The area is full of offices, so you'll have lots of bars and restaurants.
On thing that I must say is that I had a problem with the shower, spoke to the front desk about this, and in a matter of minutes I had a guy from the hotel apologizing about the inconvenient and in the meantime, 2 plumbers were fixing the shower. So in 10 minutes, the issue was solved. Customer Service is excellent.
I really recommend this hotel.