It's hard to argue with the convenience of the hotel, being across the street from Shinagawa Station. It's also a stop location for the Airport Limousine Bus, if the Narita Express isn't your thing. Within my two-week stay in Japan, I was here for my last two nights before departure in mid-August. As others have noted, check-in times are quite strict. I was lucky in having help from a clerk who did move my time up to 2pm, which was sufficient in my case. More flexibility in this would be welcome on a general level.
There are amenities and conveniences in the area, though I didn't get to check them all. There is a large area for shopping on the far side of the station that I didn't find my first day and a half, but I was still sight-seeing. One needn't worry about being able to find something nearby to fill a need.
The hotel itself is nice enough, given its age and recent refurbishment. It was the largest room I had in Japan by far with some nice views. I could see both the Tokyo Tower and Tokyo Skytree from my window (depending on clarity), and it's only two train stops to the one nearest Tokyo Tower, and another one beyond to get to the Imperial Palace. A surprising bit of quality appeared in the form of Noritake china being used for the in-room coffee/tea service.
I'm not sure why I didn't give it the fourth star, but it doesn't quite seem right. I would whole-heartedly give 3.5 on this scale. The staff were friendly and helpful, and a good cross-section of them spoke at least some helpful English. There were several dining options within the hotel, though I only tried two. My big complaint ther was that the hostess didn't check in my direction enough, and the patio (at TGI Friday's) was loud enough that no ordinary "sumimasen" could be heard. The restaurant at which I ate a lunch and a breakfast provided good food and a nice garden view. If you go for the breakfast buffet, try to go before 9:15am; it fills up rapidly after then.
Overall, though, I would recommend this hotel, especially to westerners travelling as a group or a family.
This review is the subjective opinion of a TripAdvisor member and not of TripAdvisor LLC.